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Portable Document Format (PDF), standardized as ISO 32000, is a
file format A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free. Some file form ...
developed by
Adobe Adobe ( ; ) is a building material made from earth and organic materials. is Spanish for '' mudbrick''. In some English-speaking regions of Spanish heritage, such as the Southwestern United States, the term is used to refer to any kind of ...
in 1992 to present
document A document is a written, drawn, presented, or memorialized representation of thought, often the manifestation of non-fictional, as well as fictional, content. The word originates from the Latin ''Documentum'', which denotes a "teaching" ...
s, including text formatting and images, in a manner independent of
application software Application may refer to: Mathematics and computing * Application software, computer software designed to help the user to perform specific tasks ** Application layer, an abstraction layer that specifies protocols and interface methods used in a ...
, hardware, and
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may al ...
s.Adobe Systems Incorporated
PDF Reference, Sixth edition, version 1.23 (53 MB)
Nov 2006, p. 33. Archiv

/ref> Based on the
PostScript PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, ...
language, each PDF file encapsulates a complete description of a fixed-layout flat document, including the text,
font In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a " sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design. In mod ...
s,
vector graphics Vector graphics is a form of computer graphics in which visual images are created directly from geometric shapes defined on a Cartesian plane, such as points, lines, curves and polygons. The associated mechanisms may include vector disp ...
, raster images and other information needed to display it. PDF has its roots in "The Camelot Project" initiated by Adobe co-founder
John Warnock John Edward Warnock (born October 6, 1940) is an American computer scientist and businessman best known for co-founding Adobe Systems Inc., the graphics and publishing software company, with Charles Geschke. Warnock was President of Adobe for ...
in 1991. PDF was standardized as ISO 32000 in 2008. The last edition as ISO 32000-2:2020 was published in December 2020. PDF files may contain a variety of content besides flat text and graphics including logical structuring elements, interactive elements such as annotations and form-fields, layers,
rich media Interactive media normally refers to products and services on digital computer-based systems which respond to the user's actions by presenting content such as text, moving image, animation, video and audio. Since its early conception, various ...
(including video content), three-dimensional objects using
U3D Universal 3D (U3D) is a compressed file format standard for 3D computer graphics data. The format was defined by a special consortium called ''3D Industry Forum'' that brought together a diverse group of companies and organizations, including ...
or
PRC China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones an ...
, and various other data formats. The PDF specification also provides for encryption and
digital signatures A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very high confidence that the message was created b ...
, file attachments, and
metadata Metadata is " data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive metadata – the descriptive ...
to enable workflows requiring these features.


History

Adobe Systems Adobe Inc. ( ), originally called Adobe Systems Incorporated, is an American multinational computer software company incorporated in Delaware and headquartered in San Jose, California. It has historically specialized in software for the c ...
made the PDF specification available free of charge in 1993. In the early years PDF was popular mainly in
desktop publishing Desktop publishing (DTP) is the creation of documents using page layout software on a personal ("desktop") computer. It was first used almost exclusively for print publications, but now it also assists in the creation of various forms of online ...
workflow A workflow consists of an orchestrated and repeatable pattern of activity, enabled by the systematic organization of resources into processes that transform materials, provide services, or process information. It can be depicted as a sequence of ...
s, and competed with a variety of formats such as
DjVu DjVu ( , like French " déjà vu") is a computer file format designed primarily to store scanned documents, especially those containing a combination of text, line drawings, indexed color images, and photographs. It uses technologies such as im ...
,
Envoy Envoy or Envoys may refer to: Diplomacy * Diplomacy, in general * Envoy (title) * Special envoy, a type of diplomatic rank Brands * Airspeed Envoy, a 1930s British light transport aircraft * Envoy (automobile), an automobile brand used to sell B ...
, Common Ground Digital Paper, Farallon Replica and even Adobe's own
PostScript PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, ...
format. PDF was a
proprietary format A proprietary file format is a file format of a company, organization, or individual that contains data that is ordered and stored according to a particular encoding-scheme, designed by the company or organization to be secret, such that the decodi ...
controlled by Adobe until it was released as an
open standard An open standard is a standard that is openly accessible and usable by anyone. It is also a prerequisite to use open license, non-discrimination and extensibility. Typically, anybody can participate in the development. There is no single definiti ...
on July 1, 2008, and published by the
International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in A ...
as ISO 32000-1:2008, at which time control of the specification passed to an ISO Committee of volunteer industry experts. In 2008, Adobe published a Public Patent License to ISO 32000-1 granting
royalty-free Royalty-free (RF) material subject to copyright or other intellectual property rights may be used without the need to pay royalties or license fees for each use, per each copy or volume sold or some time period of use or sales. Computer standards ...
rights for all patents owned by Adobe that are necessary to make, use, sell, and distribute PDF-compliant implementations. PDF 1.7, the sixth edition of the PDF specification that became ISO 32000-1, includes some proprietary technologies defined only by Adobe, such as
Adobe XML Forms Architecture XFA (also known as XFA forms) stands for XML Forms Architecture, a family of proprietary XML specifications that was suggested and developed by JetForm to enhance the processing of web forms. It can be also used in PDF files starting with the ...
(XFA) and
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
extension for Acrobat, which are referenced by ISO 32000-1 as
normative Normative generally means relating to an evaluative standard. Normativity is the phenomenon in human societies of designating some actions or outcomes as good, desirable, or permissible, and others as bad, undesirable, or impermissible. A norm in ...
and indispensable for the full implementation of the ISO 32000-1 specification. These proprietary technologies are not standardized and their specification is published only on Adobe's website. Many of them are also not supported by popular third-party implementations of PDF. In December 2020, the second edition of PDF 2.0, ISO 32000-2:2020, was published, including clarifications, corrections and critical updates to normative references. ISO 32000-2 does not include any proprietary technologies as normative references.


Technical details

A PDF file is often a combination of
vector graphics Vector graphics is a form of computer graphics in which visual images are created directly from geometric shapes defined on a Cartesian plane, such as points, lines, curves and polygons. The associated mechanisms may include vector disp ...
, text, and bitmap graphics. The basic types of content in a PDF are: * Typeset text stored as content streams (i.e., not encoded in
plain text In computing, plain text is a loose term for data (e.g. file contents) that represent only characters of readable material but not its graphical representation nor other objects ( floating-point numbers, images, etc.). It may also include a li ...
); * Vector graphics for illustrations and designs that consist of shapes and lines; * Raster graphics for photographs and other types of images * Multimedia objects in the document. In later PDF revisions, a PDF document can also support links (inside document or web page), forms,
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
(initially available as a plugin for Acrobat 3.0), or any other types of embedded contents that can be handled using plug-ins. PDF combines three technologies: * An equivalent subset of the
PostScript PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, ...
page description programming language but in declarative form, for generating the layout and graphics. * A font-embedding/replacement system to allow fonts to travel with the documents. * A structured storage system to bundle these elements and any associated content into a single file, with
data compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compress ...
where appropriate.


PostScript language

PostScript PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, ...
is a
page description language In digital printing, a page description language (PDL) is a computer language that describes the appearance of a printed page in a higher level than an actual output bitmap (or generally raster graphics). An overlapping term is printer control ...
run in an interpreter to generate an image, a process requiring many resources. It can handle graphics and standard features of
programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programmin ...
s such as if statements and loop commands. PDF is largely based on PostScript but simplified to remove flow control features like these, while graphics commands equivalent to lineto remain. Historically, the PostScript-like PDF code is generated from a source PostScript file. The graphics commands that are output by the PostScript code are collected and tokenized. Any files, graphics, or fonts to which the document refers also are collected. Then, everything is compressed to a single file. Therefore, the entire PostScript world (fonts, layout, measurements) remains intact. As a document format, PDF has several advantages over PostScript: * PDF contains tokenized and interpreted results of the PostScript source code, for direct correspondence between changes to items in the PDF page description and changes to the resulting page appearance. * PDF (from version 1.4) supports transparent graphics; PostScript does not. * PostScript is an interpreted programming language with an implicit global state, so instructions accompanying the description of one page can affect the appearance of any following page. Therefore, all preceding pages in a PostScript document must be processed to determine the correct appearance of a given page, whereas each page in a PDF document is unaffected by the others. As a result, PDF viewers allow the user to quickly jump to the final pages of a long document, whereas a PostScript viewer needs to process all pages sequentially before being able to display the destination page (unless the optional PostScript Document Structuring Conventions have been carefully compiled and included). PDF 1.6 and later supports interactive 3D documents embedded in a PDF file: 3D drawings can be embedded using
U3D Universal 3D (U3D) is a compressed file format standard for 3D computer graphics data. The format was defined by a special consortium called ''3D Industry Forum'' that brought together a diverse group of companies and organizations, including ...
or
PRC China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones an ...
and various other data formats.


File format

A PDF file is organized using
ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because ...
characters, except for certain elements that may have binary content. The file starts with a header containing a magic number (as a readable string) and the version of the format, for example %PDF-1.7. The format is a subset of a COS ("Carousel" Object Structure) format. A COS tree file consists primarily of ''objects'', of which there are nine types: *
Boolean Any kind of logic, function, expression, or theory based on the work of George Boole is considered Boolean. Related to this, "Boolean" may refer to: * Boolean data type, a form of data with only two possible values (usually "true" and "false" ...
values, representing ''true'' or ''false'' *
Real numbers In mathematics, a real number is a number that can be used to measure a ''continuous'' one- dimensional quantity such as a distance, duration or temperature. Here, ''continuous'' means that values can have arbitrarily small variations. Ever ...
*
Integers An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign ( −1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the languag ...
* Strings, enclosed within parentheses ((...)) or represented as hexadecimal within single angle brackets (<...>). Strings may contain 8-bit characters. * Names, starting with a forward slash (/) *
Arrays An array is a systematic arrangement of similar objects, usually in rows and columns. Things called an array include: {{TOC right Music * In twelve-tone and serial composition, the presentation of simultaneous twelve-tone sets such that the ...
, ordered collections of objects enclosed within square brackets ( ../code>) *
Dictionaries A dictionary is a listing of lexemes from the lexicon of one or more specific languages, often arranged alphabetically (or by radical and stroke for ideographic languages), which may include information on definitions, usage, etymologi ...
, collections of objects indexed by names enclosed within double angle brackets (<<...>>) *
Streams A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams ...
, usually containing large amounts of optionally compressed binary data, preceded by a dictionary and enclosed between the stream and endstream keywords. * The null object Furthermore, there may be comments, introduced with the percent sign (%). Comments may contain 8-bit characters. Objects may be either ''direct'' (embedded in another object) or ''indirect''. Indirect objects are numbered with an ''object number'' and a ''generation number'' and defined between the obj and endobj keywords if residing in the document root. Beginning with PDF version 1.5, indirect objects (except other streams) may also be located in special streams known as ''object streams'' (marked /Type /ObjStm). This technique enables non-stream objects to have standard stream filters applied to them, reduces the size of files that have large numbers of small indirect objects and is especially useful for ''Tagged PDF''. Object streams do not support specifying an object's ''generation number'' (other than 0). An index table, also called the cross-reference table, is located near the end of the file and gives the byte offset of each indirect object from the start of the file. This design allows for efficient
random access Random access (more precisely and more generally called direct access) is the ability to access an arbitrary element of a sequence in equal time or any datum from a population of addressable elements roughly as easily and efficiently as any othe ...
to the objects in the file, and also allows for small changes to be made without rewriting the entire file (''incremental update''). Before PDF version 1.5, the table would always be in a special ASCII format, be marked with the xref keyword, and follow the main body composed of indirect objects. Version 1.5 introduced optional ''cross-reference streams'', which have the form of a standard stream object, possibly with filters applied. Such a stream may be used instead of the ASCII cross-reference table and contains the offsets and other information in binary format. The format is flexible in that it allows for integer width specification (using the /W array), so that for example, a document not exceeding 64 
KiB The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...
in size may dedicate only 2  bytes for object offsets. At the end of a PDF file is a footer containing * The startxref keyword followed by an offset to the start of the cross-reference table (starting with the xref keyword) or the cross-reference stream object, followed by * The %%EOF
end-of-file In computing, end-of-file (EOF) is a condition in a computer operating system where no more data can be read from a data source. The data source is usually called a file or stream. Details In the C standard library, the character reading funct ...
marker. If a cross-reference stream is not being used, the footer is preceded by the trailer keyword followed by a dictionary containing information that would otherwise be contained in the cross-reference stream object's dictionary: * A reference to the root object of the tree structure, also known as the ''catalog'' (/Root) * The count of indirect objects in the cross-reference table (/Size) * Other optional information Within each page, there are one or multiple content streams that describe the text, vector and images being drawn on the page. The content stream is stack-based, similar to
PostScript PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, ...
. There are two layouts to the PDF files: non-linearized (not "optimized") and linearized ("optimized"). Non-linearized PDF files can be smaller than their linear counterparts, though they are slower to access because portions of the data required to assemble pages of the document are scattered throughout the PDF file. Linearized PDF files (also called "optimized" or "web optimized" PDF files) are constructed in a manner that enables them to be read in a Web browser plugin without waiting for the entire file to download, since all objects required for the first page to display are optimally organized at the start of the file. PDF files may be optimized using
Adobe Acrobat Adobe Acrobat is a family of application software and Web services developed by Adobe Inc. to view, create, manipulate, print and manage Portable Document Format (PDF) files. The family comprises Acrobat Reader (formerly Reader), Acrobat (former ...
software or QPDF.


Imaging model

The basic design of how
graphics Graphics () are visual images or designs on some surface, such as a wall, canvas, screen, paper, or stone, to inform, illustrate, or entertain. In contemporary usage, it includes a pictorial representation of data, as in design and manufac ...
are represented in PDF is very similar to that of
PostScript PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, ...
, except for the use of transparency, which was added in PDF 1.4. PDF graphics use a device-independent
Cartesian coordinate system A Cartesian coordinate system (, ) in a plane is a coordinate system that specifies each point uniquely by a pair of numerical coordinates, which are the signed distances to the point from two fixed perpendicular oriented lines, measured i ...
to describe the surface of a page. A
PDF Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...
page description can use a
matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
to scale,
rotate Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...
, or
skew Skew may refer to: In mathematics * Skew lines, neither parallel nor intersecting. * Skew normal distribution, a probability distribution * Skew field or division ring * Skew-Hermitian matrix * Skew lattice * Skew polygon, whose vertices do ...
graphical elements. A key concept in PDF is that of the ''graphics state'', which is a collection of graphical parameters that may be changed, saved, and restored by a ''page description''. PDF has (as of version 2.0) 25 graphics state properties, of which some of the most important are: * The ''current transformation matrix'' (CTM), which determines the coordinate system * The '' clipping path'' * The ''
color space A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of colorwhether such representation entails an analog or a digital represe ...
'' * The '' alpha constant'', which is a key component of transparency *'' Black point compensation'' control (introduced in PDF 2.0)


Vector graphics

As in
PostScript PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, ...
,
vector graphics Vector graphics is a form of computer graphics in which visual images are created directly from geometric shapes defined on a Cartesian plane, such as points, lines, curves and polygons. The associated mechanisms may include vector disp ...
in PDF are constructed with ''paths''. Paths are usually composed of lines and cubic Bézier curves, but can also be constructed from the outlines of text. Unlike
PostScript PostScript (PS) is a page description language in the electronic publishing and desktop publishing realm. It is a dynamically typed, concatenative programming language. It was created at Adobe Systems by John Warnock, Charles Geschke, ...
, PDF does not allow a single path to mix text outlines with lines and curves. Paths can be stroked, filled, fill then stroked, or used for
clipping Clipping may refer to: Words * Clipping (morphology), the formation of a new word by shortening it, e.g. "ad" from "advertisement" * Clipping (phonetics), shortening the articulation of a speech sound, usually a vowel * Clipping (publication ...
. Strokes and fills can use any color set in the graphics state, including ''patterns''. PDF supports several types of patterns. The simplest is the ''tiling pattern'' in which a piece of artwork is specified to be drawn repeatedly. This may be a ''colored tiling pattern'', with the colors specified in the pattern object, or an ''uncolored tiling pattern'', which defers color specification to the time the pattern is drawn. Beginning with PDF 1.3 there is also a ''shading pattern'', which draws continuously varying colors. There are seven types of shading patterns of which the simplest are the ''axial shading'' (Type 2) and ''radial shading'' (Type 3).


Raster images

Raster images in PDF (called ''Image XObjects'') are represented by dictionaries with an associated stream. The dictionary describes the properties of the image, and the stream contains the image data. (Less commonly, small raster images may be embedded directly in a page description as an ''inline image''.) Images are typically ''filtered'' for compression purposes. Image filters supported in PDF include the following general-purpose filters: * ''ASCII85Decode'', a filter used to put the stream into 7-bit
ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because ...
, * ''ASCIIHexDecode'', similar to ASCII85Decode but less compact, * ''FlateDecode'', a commonly used filter based on the deflate algorithm defined in (deflate is also used in the
gzip gzip is a file format and a software application used for file compression and decompression. The program was created by Jean-loup Gailly and Mark Adler as a free software replacement for the compress program used in early Unix systems, an ...
, PNG, and zip file formats among others); introduced in PDF 1.2; it can use one of two groups of predictor functions for more compact zlib/deflate compression: ''Predictor 2'' from the
TIFF Tag Image File Format, abbreviated TIFF or TIF, is an image file format for storing raster graphics images, popular among graphic artists, the publishing industry, and photographers. TIFF is widely supported by scanning, faxing, word process ...
6.0 specification and predictors (filters) from the PNG specification (), * ''LZWDecode'', a filter based on LZW Compression; it can use one of two groups of predictor functions for more compact LZW compression: ''Predictor 2'' from the TIFF 6.0 specification and predictors (filters) from the PNG specification, * ''RunLengthDecode'', a simple compression method for streams with repetitive data using the
run-length encoding Run-length encoding (RLE) is a form of lossless data compression in which ''runs'' of data (sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original ...
algorithm and the image-specific filters, * ''DCTDecode'', a
lossy In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size ...
filter based on the
JPEG JPEG ( ) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and i ...
standard, * ''CCITTFaxDecode'', a
lossless Lossless compression is a class of data compression that allows the original data to be perfectly reconstructed from the compressed data with no loss of information. Lossless compression is possible because most real-world data exhibits statistic ...
bi-level (black/white) filter based on the Group 3 or Group 4
CCITT The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Comm ...
(ITU-T) fax compression standard defined in ITU-T T.4 and T.6, * ''JBIG2Decode'', a lossy or lossless bi-level (black/white) filter based on the JBIG2 standard, introduced in PDF 1.4, and * ''JPXDecode'', a lossy or lossless filter based on the
JPEG 2000 JPEG 2000 (JP2) is an image compression standard and coding system. It was developed from 1997 to 2000 by a Joint Photographic Experts Group committee chaired by Touradj Ebrahimi (later the JPEG president), with the intention of superseding th ...
standard, introduced in PDF 1.5. Normally all image content in a PDF is embedded in the file. But PDF allows image data to be stored in external files by the use of ''external streams'' or ''Alternate Images''. Standardized subsets of PDF, including
PDF/A PDF/A is an ISO-standardized version of the Portable Document Format (PDF) specialized for use in the archiving and long-term preservation of electronic documents. PDF/A differs from PDF by prohibiting features unsuitable for long-term archivin ...
and PDF/X, prohibit these features.


Text

Text in PDF is represented by ''text elements'' in page content streams. A text element specifies that ''characters'' should be drawn at certain positions. The characters are specified using the ''encoding'' of a selected ''font resource''. A font object in PDF is a description of a digital
typeface A typeface (or font family) is the design of lettering that can include variations in size, weight (e.g. bold), slope (e.g. italic), width (e.g. condensed), and so on. Each of these variations of the typeface is a font. There are thousands ...
. It may either describe the characteristics of a typeface, or it may include an embedded ''font file''. The latter case is called an ''embedded font'' while the former is called an ''unembedded font''. The font files that may be embedded are based on widely used standard digital font formats: Type 1 (and its compressed variant CFF),
TrueType TrueType is an outline font standard developed by Apple in the late 1980s as a competitor to Adobe's Type 1 fonts used in PostScript. It has become the most common format for fonts on the classic Mac OS, macOS, and Microsoft Windows opera ...
, and (beginning with PDF 1.6)
OpenType OpenType is a format for scalable computer fonts. It was built on its predecessor TrueType, retaining TrueType's basic structure and adding many intricate data structures for prescribing typographic behavior. OpenType is a registered trademark ...
. Additionally PDF supports the Type 3 variant in which the components of the font are described by PDF graphic operators. Fourteen typefaces, known as the ''standard 14 fonts'', have a special significance in PDF documents: * Times (v3) (in regular, italic, bold, and bold italic) *
Courier A courier is a person or organisation that delivers a message, package or letter from one place or person to another place or person. Typically, a courier provides their courier service on a commercial contract basis; however, some couriers are ...
(in regular, oblique, bold and bold oblique) *
Helvetica Helvetica (originally Neue Haas Grotesk) is a widely used sans-serif typeface developed in 1957 by Swiss typeface designer Max Miedinger and Eduard Hoffmann. Helvetica is a neo-grotesque design, one influenced by the famous 19th century (1890 ...
(v3) (in regular, oblique, bold and bold oblique) *
Symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different con ...
* Zapf Dingbats These fonts are sometimes called the ''base fourteen fonts''. These fonts, or suitable substitute fonts with the same metrics, should be available in most PDF readers, but they are not ''guaranteed'' to be available in the reader, and may only display correctly if the system has them installed. Fonts may be substituted if they are not embedded in a PDF. Within text strings, characters are shown using ''character codes'' (integers) that map to glyphs in the current font using an ''encoding''. There are several predefined encodings, including ''WinAnsi'', ''MacRoman'', and many encodings for East Asian languages and a font can have its own built-in encoding. (Although the WinAnsi and MacRoman encodings are derived from the historical properties of the
Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for se ...
and
Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and software e ...
operating systems, fonts using these encodings work equally well on any platform.) PDF can specify a predefined encoding to use, the font's built-in encoding or provide a lookup table of differences to a predefined or built-in encoding (not recommended with TrueType fonts). The encoding mechanisms in PDF were designed for Type 1 fonts, and the rules for applying them to TrueType fonts are complex. For large fonts or fonts with non-standard glyphs, the special encodings ''Identity-H'' (for horizontal writing) and ''Identity-V'' (for vertical) are used. With such fonts, it is necessary to provide a ''ToUnicode'' table if semantic information about the characters is to be preserved.


Transparency

The original imaging model of PDF was, like PostScript's, ''opaque'': each object drawn on the page completely replaced anything previously marked in the same location. In PDF 1.4 the imaging model was extended to allow transparency. When transparency is used, new objects interact with previously marked objects to produce blending effects. The addition of transparency to PDF was done by means of new extensions that were designed to be ignored in products written to PDF 1.3 and earlier specifications. As a result, files that use a small amount of transparency might view acceptably by older viewers, but files making extensive use of transparency could be viewed incorrectly by an older viewer. The transparency extensions are based on the key concepts of ''transparency groups'', ''blending modes'', ''shape'', and ''alpha''. The model is closely aligned with the features of
Adobe Illustrator Adobe Illustrator is a vector graphics editor and design program developed and marketed by Adobe Inc. Originally designed for the Apple Macintosh, development of Adobe Illustrator began in 1985. Along with Creative Cloud (Adobe's shift to m ...
version 9. The blend modes were based on those used by
Adobe Photoshop Adobe Photoshop is a raster graphics editor developed and published by Adobe Inc. for Windows and macOS. It was originally created in 1988 by Thomas and John Knoll. Since then, the software has become the industry standard not only in r ...
at the time. When the PDF 1.4 specification was published, the formulas for calculating blend modes were kept secret by Adobe. They have since been published. The concept of a transparency group in PDF specification is independent of existing notions of "group" or "layer" in applications such as Adobe Illustrator. Those groupings reflect logical relationships among objects that are meaningful when editing those objects, but they are not part of the imaging model.


Additional features


Logical structure and accessibility

A "tagged" PDF (see clause 14.8 in ISO 32000) includes document structure and semantics information to enable reliable text extraction and
accessibility Accessibility is the design of products, devices, services, vehicles, or environments so as to be usable by people with disabilities. The concept of accessible design and practice of accessible development ensures both "direct access" (i. ...
. Technically speaking, tagged PDF is a stylized use of the format that builds on the logical structure framework introduced in PDF 1.3. Tagged PDF defines a set of standard structure types and attributes that allow page content (text, graphics, and images) to be extracted and reused for other purposes. Tagged PDF is not required in situations where a PDF file is intended only for print. Since the feature is optional, and since the rules for Tagged PDF were relatively vague in ISO 32000-1, support for tagged PDF amongst consuming devices, including
assistive technology Assistive technology (AT) is a term for assistive, adaptive, and rehabilitative devices for people with disabilities and the elderly. Disabled people often have difficulty performing activities of daily living (ADLs) independently, or even wi ...
(AT), is uneven as of 2021. ISO 32000-2, however, includes an improved discussion of tagged PDF which is anticipated to facilitate further adoption. An ISO-standardized subset of PDF specifically targeted at accessibility,
PDF/UA PDF/UA (PDF/Universal Accessibility), formally ISO 14289, is an International Organization for Standardization (ISO) standard for accessible PDF technology. A technical specification intended for developers implementing PDF writing and processing ...
, was first published in 2012.


Optional Content Groups (layers)

With the introduction of PDF version, 1.5 (2003) came the concept of Layers. Layers, or as they are more formally known Optional Content Groups (OCGs), refer to sections of content in a PDF document that can be selectively viewed or hidden by document authors or viewers. This capability is useful in CAD drawings, layered artwork, maps, multi-language documents, etc. Basically, it consists of an Optional Content Properties Dictionary added to the document root. This dictionary contains an array of Optional Content Groups (OCGs), each describing a set of information and each of which may be individually displayed or suppressed, plus a set of Optional Content Configuration Dictionaries, which give the status (Displayed or Suppressed) of the given OCGs.


Encryption and signatures

A PDF file may be
encrypted In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can de ...
, for security, in which case a password is needed to view or edit the contents. PDF 2.0 defines 256-bit AES encryption as standard for PDF 2.0 files. The PDF Reference also defines ways that third parties can define their own encryption systems for PDF. PDF files may be digitally signed, to provide secure authentication; complete details on implementing digital signatures in PDF is provided in ISO 32000-2. PDF files may also contain embedded
DRM DRM may refer to: Government, military and politics * Defense reform movement, U.S. campaign inspired by Col. John Boyd * Democratic Republic of Madagascar, a former socialist state (1975–1992) on Madagascar * Direction du renseignement milit ...
restrictions that provide further controls that limit copying, editing or printing. These restrictions depend on the reader software to obey them, so the security they provide is limited. The standard security provided by PDF consists of two different methods and two different passwords: a ''user password'', which encrypts the file and prevents opening, and an ''owner password'', which specifies operations that should be restricted even when the document is decrypted, which can include modifying, printing, or copying text and graphics out of the document, or adding or modifying text notes and AcroForm fields. The user password encrypts the file, while the owner password does not, instead relying on client software to respect these restrictions. An owner password can easily be removed by software, including some free online services. Thus, the use restrictions that a document author places on a PDF document are not secure, and cannot be assured once the file is distributed; this warning is displayed when applying such restrictions using
Adobe Acrobat Adobe Acrobat is a family of application software and Web services developed by Adobe Inc. to view, create, manipulate, print and manage Portable Document Format (PDF) files. The family comprises Acrobat Reader (formerly Reader), Acrobat (former ...
software to create or edit PDF files. Even without removing the password, most freeware or open source PDF readers ignore the permission "protections" and allow the user to print or make copy of excerpts of the text as if the document were not limited by password protection. Beginning with PDF 1.5, Usage rights (UR) signatures are used to enable additional interactive features that are not available by default in a particular PDF viewer application. The signature is used to validate that the permissions have been granted by a
bona fide In human interactions, good faith ( la, bona fides) is a sincere intention to be fair, open, and honest, regardless of the outcome of the interaction. Some Latin phrases have lost their literal meaning over centuries, but that is not the case ...
granting authority. For example, it can be used to allow a user: * To save the PDF document along with a modified form and/or annotation data * Import form data files in FDF, XFDF, and text (CSV/TSV) formats * Export form data files in FDF and XFDF formats * Submit form data *
Instantiate Instantiation or instance may refer to: Philosophy * A modern concept similar to ''participation'' in classical Platonism; see the Theory of Forms * The instantiation principle, the idea that in order for a property to exist, it must be had by ...
new pages from named page templates * Apply a
digital signature A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very high confidence that the message was created b ...
to existing digital signature form field * Create, delete, modify, copy, import, and export annotations For example, Adobe Systems grants permissions to enable additional features in Adobe Reader, using
public-key cryptography Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic a ...
. Adobe Reader verifies that the signature uses a
certificate Certificate may refer to: * Birth certificate * Marriage certificate * Death certificate * Gift certificate * Certificate of authenticity, a document or seal certifying the authenticity of something * Certificate of deposit, or CD, a financial ...
from an Adobe-authorized certificate authority. Any PDF application can use this same mechanism for its own purposes. Under specific circumstances including non-
patched Patched (Ptc) is a conserved 12-pass transmembrane protein receptor that plays an obligate negative regulatory role in the Hedgehog signaling pathway in insects and vertebrates. Patched is an essential gene in embryogenesis for proper segme ...
systems of the receiver, the information the receiver of a digital signed document sees can be manipulated by the sender after the document has been signed by the signer.
PAdES PAdES (''PDF Advanced Electronic Signatures'') is a set of restrictions and extensions to PDF and ISO 32000-1 making it suitable for advanced electronic signatures. This is published by ETSI as EN 319 142. Description While PDF and ISO 32000 ...
(''PDF Advanced Electronic Signatures'') is a set of restrictions and extensions to PDF and ISO 32000-1 making it suitable for advanced electronic signatures. This is published by
ETSI The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standar ...
as TS 102 778.


File attachments

PDF files can have file attachments which processors may access and open or save to a local filesystem.


Metadata

PDF files can contain two types of metadata. The first is the Document Information Dictionary, a set of key/value fields such as author, title, subject, creation and update dates. This is optional and is referenced from Info key in the trailer of the file. A small set of fields is defined and can be extended with additional text values if required. This method is deprecated in PDF 2.0. In PDF 1.4, support was added for Metadata Streams, using the
Extensible Metadata Platform The Extensible Metadata Platform (XMP) is an ISO standard, originally created by Adobe Systems Inc., for the creation, processing and interchange of standardized and custom metadata for digital documents and data sets. XMP standardizes a dat ...
(XMP) to add XML standards-based extensible metadata as used in other file formats. PDF 2.0 allows metadata to be attached to any object in the document, such as information about embedded illustrations, fonts, images as well as the whole document (attaching to the document catalog), using an extensible schema. PDF documents can also contain display settings, including the page display layout and zoom level in a Viewer Preferences object. Adobe Reader uses these settings to override the user's default settings when opening the document. The free Adobe Reader cannot remove these settings.


Accessibility

PDF files can be created specifically to be accessible for people with disabilities. PDF file formats in use can include tags, text equivalents, captions, audio descriptions, and more. Some software can automatically produce tagged PDFs, but this feature is not always enabled by default. Leading
screen reader A screen reader is a form of assistive technology (AT) that renders text and image content as speech or braille output. Screen readers are essential to people who are blind, and are useful to people who are visually impaired, illiterate, or ...
s, including JAWS, Window-Eyes, Hal, and Kurzweil 1000 and 3000 can read tagged PDF. Moreover, tagged PDFs can be re-flowed and magnified for readers with visual impairments. Adding tags to older PDFs and those that are generated from scanned documents can present some challenges. One of the significant challenges with PDF accessibility is that PDF documents have three distinct views, which, depending on the document's creation, can be inconsistent with each other. The three views are (i) the physical view, (ii) the tags view, and (iii) the content view. The physical view is displayed and printed (what most people consider a PDF document). The tags view is what screen readers and other assistive technologies use to deliver high-quality navigation and reading experience to users with disabilities. The content view is based on the physical order of objects within the PDF's content stream and may be displayed by software that does not fully support the tags' view, such as the Reflow feature in Adobe's Reader.
PDF/UA PDF/UA (PDF/Universal Accessibility), formally ISO 14289, is an International Organization for Standardization (ISO) standard for accessible PDF technology. A technical specification intended for developers implementing PDF writing and processing ...
, the International Standard for accessible PDF based on ISO 32000-1 was first published as ISO 14289–1 in 2012 and establishes normative language for accessible PDF technology.


Multimedia

''Rich Media PDF'' is a PDF file including interactive content that can be embedded or linked within the file. It can contain images, audio, video content or buttons. For example, if the interactive PDF is a digital catalog for an E-commerce business, products can be listed on the PDF pages, can be added images, links to the website and buttons to order directly from there.


Forms

''Interactive Forms'' is a mechanism to add forms to the PDF file format. PDF currently supports two different methods for integrating data and PDF forms. Both formats today coexist in the PDF specification: * AcroForms (also known as Acrobat forms), introduced in the PDF 1.2 format specification and included in all later PDF specifications. * XML Forms Architecture (XFA) forms, introduced in the PDF 1.5 format specification. Adobe XFA Forms are not compatible with AcroForms. XFA was deprecated from PDF with PDF 2.0. AcroForms were introduced in the PDF 1.2 format. AcroForms permit using objects (''e.g.''
text box type=search placeholder=An example text box, which can be used to search the English Wikipedia. A text box (input box), text field or text entry box is a control element of a graphical user interface, that should enable the user to input ...
es,
Radio button A radio button or option button is a graphical control element that allows the user to choose only one of a predefined set of mutually exclusive options. The singular property of a radio button makes it distinct from checkboxes, where the user ...
s, ''etc.'') and some code (''e.g.''
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...
). Alongside the standard PDF action types, interactive forms (AcroForms) support submitting, resetting, and importing data. The "submit" action transmits the names and values of selected interactive form fields to a specified uniform resource locator (URL). Interactive form field names and values may be submitted in any of the following formats, (depending on the settings of the action's ExportFormat, SubmitPDF, and XFDF flags): ; HTML Form format: HTML 4.01 Specification since PDF 1.5; HTML 2.0 since 1.2 ; Forms Data Format (FDF): based on PDF, uses the same syntax and has essentially the same file structure, but is much simpler than PDF since the body of an FDF document consists of only one required object. Forms Data Format is defined in the PDF specification (since PDF 1.2). The Forms Data Format can be used when submitting form data to a server, receiving the response, and incorporating it into the interactive form. It can also be used to export form data to stand-alone files that can be imported back into the corresponding PDF interactive form. FDF was originally defined in 1996 as part of ISO 32000-2:2017. ; XML Forms Data Format (XFDF): (external XML Forms Data Format Specification, Version 2.0; supported since PDF 1.5; it replaced the "XML" form submission format defined in PDF 1.4) the XML version of Forms Data Format, but the XFDF implements only a subset of FDF containing forms and annotations. Some entries in the FDF dictionary do not have XFDF equivalents – such as the Status, Encoding, JavaScript, Page's keys, EmbeddedFDFs, Differences, and Target. In addition, XFDF does not allow the spawning, or addition, of new pages based on the given data; as can be done when using an FDF file. The XFDF specification is referenced (but not included) in PDF 1.5 specification (and in later versions). It is described separately in ''XML Forms Data Format Specification''. The PDF 1.4 specification allowed form submissions in XML format, but this was replaced by submissions in XFDF format in the PDF 1.5 specification. XFDF conforms to the XML standard. XFDF can be used in the same way as FDF; e.g., form data is submitted to a server, modifications are made, then sent back and the new form data is imported in an interactive form. It can also be used to export form data to stand-alone files that can be imported back into the corresponding PDF interactive form. As of August, 2019, XFDF 3.0 is an ISO/IEC standard under the formal name ''ISO 19444-1:2019 - Document management — XML Forms Data Format — Part 1: Use of ISO 32000-2 (XFDF 3.0)''. This standard is a normative reference of ISO 32000-2. ; PDF The entire document can be submitted rather than individual fields and values, as was defined in PDF 1.4. AcroForms can keep form field values in external stand-alone files containing key-value pairs. The external files may use Forms Data Format (FDF) and XML Forms Data Format (XFDF) files. The usage rights (UR) signatures define rights for import form data files in FDF, XFDF and text ( CSV/ TSV) formats, and export form data files in FDF and XFDF formats. In PDF 1.5, Adobe Systems introduced a proprietary format for forms;
Adobe XML Forms Architecture XFA (also known as XFA forms) stands for XML Forms Architecture, a family of proprietary XML specifications that was suggested and developed by JetForm to enhance the processing of web forms. It can be also used in PDF files starting with the ...
(XFA). Adobe XFA Forms are not compatible with ISO 32000's AcroForms feature, and most PDF processors do not handle XFA content. The XFA specification is referenced from ISO 32000-1/PDF 1.7 as an external proprietary specification, and was entirely deprecated from PDF with ISO 32000-2 (PDF 2.0).


Licensing

Anyone may create applications that can read and write PDF files without having to pay royalties to
Adobe Systems Adobe Inc. ( ), originally called Adobe Systems Incorporated, is an American multinational computer software company incorporated in Delaware and headquartered in San Jose, California. It has historically specialized in software for the c ...
; Adobe holds patents to PDF, but licenses them for
royalty-free Royalty-free (RF) material subject to copyright or other intellectual property rights may be used without the need to pay royalties or license fees for each use, per each copy or volume sold or some time period of use or sales. Computer standards ...
use in developing software complying with its PDF specification.


Security

In November 2019, researchers from
Ruhr University Bochum The Ruhr University Bochum (, ) is a public research university located in the southern hills of the central Ruhr area, Bochum, Germany. It was founded in 1962 as the first new public university in Germany after World War II. Instruction began in ...
and Hackmanit GmbH published attacks on digitally signed PDFs . They showed how to change the visible content in a signed PDF without invalidating the signature in 21 of 22 desktop PDF viewers and 6 of 8 online validation services by abusing implementation flaws. At the same conference, they additionally showed how to exfiltrate the plaintext of encrypted content in PDFs. In 2021, they showed new so-called ''shadow attacks'' on PDFs that abuse the flexibility of features provided in the specification. An overview of security issues in PDFs regarding
denial of service In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host conne ...
, information disclosure, data manipulation, and
Arbitrary code execution In computer security, arbitrary code execution (ACE) is an attacker's ability to run any commands or code of the attacker's choice on a target machine or in a target process. An arbitrary code execution vulnerability is a security flaw in softw ...
attacks was presented by Jens Müller. PDF attachments carrying viruses were first discovered in 2001. The virus, named ''OUTLOOK.PDFWorm'' or ''Peachy'', uses
Microsoft Outlook Microsoft Outlook is a personal information manager software system from Microsoft, available as a part of the Microsoft Office and Microsoft 365 software suites. Though primarily an email client, Outlook also includes such functions as c ...
to send itself as an attached Adobe PDF file. It was activated with Adobe Acrobat, but not with Acrobat Reader. From time to time, new vulnerabilities are discovered in various versions of Adobe Reader, prompting the company to issue security fixes. Other PDF readers are also susceptible. One aggravating factor is that a PDF reader can be configured to start automatically if a web page has an embedded PDF file, providing a vector for attack. If a malicious web page contains an infected PDF file that takes advantage of a vulnerability in the PDF reader, the system may be compromised even if the browser is secure. Some of these vulnerabilities are a result of the PDF standard allowing PDF documents to be scripted with JavaScript. Disabling JavaScript execution in the PDF reader can help mitigate such future exploits, although it does not protect against exploits in other parts of the PDF viewing software. Security experts say that JavaScript is not essential for a PDF reader and that the security benefit that comes from disabling JavaScript outweighs any compatibility issues caused. One way of avoiding PDF file exploits is to have a local or web service convert files to another format before viewing. On March 30, 2010 security researcher Didier Stevens reported an Adobe Reader and Foxit Reader exploit that runs a malicious executable if the user allows it to launch when asked.


Software


Viewers and editors

PDF viewers are generally provided free of charge, and many versions are available from a variety of sources. There are many software options for creating PDFs, including the PDF printing capabilities built into
macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...
,
iOS iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also include ...
, and most
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, wh ...
distributions,
LibreOffice LibreOffice () is a free and open-source office productivity software suite, a project of The Document Foundation (TDF). It was forked in 2010 from OpenOffice.org, an open-sourced version of the earlier StarOffice. The LibreOffice suite c ...
,
Microsoft Office 2007 Microsoft Office 2007 (codenamed Office 12) is an office suite for Windows, developed and published by Microsoft. It was officially revealed on March 9, 2006 and was the 12th version of Microsoft Office. It was released to manufacturing on Novemb ...
(if updated to SP2) and later, WordPerfect 9,
Scribus Scribus () is free and open-source desktop publishing (DTP) software available for most desktop operating systems. It is designed for layout, typesetting, and preparation of files for professional-quality image-setting equipment. Scribus can ...
, numerous PDF print drivers for Microsoft Windows, the
pdfTeX __NOTOC__ The computer program pdfTeX is an extension of Knuth's typesetting program TeX, and was originally written and developed into a publicly usable product by Hàn Thế Thành as a part of the work for his PhD thesis at the Faculty of ...
typesetting system, the
DocBook DocBook is a semantic markup language for technical documentation. It was originally intended for writing technical documents related to computer hardware and software, but it can be used for any other sort of documentation. As a semantic languag ...
PDF tools, applications developed around
Ghostscript Ghostscript is a suite of software based on an interpreter for Adobe Systems' PostScript and Portable Document Format (PDF) page description languages. Its main purposes are the rasterization or rendering of such page description language files ...
and
Adobe Acrobat Adobe Acrobat is a family of application software and Web services developed by Adobe Inc. to view, create, manipulate, print and manage Portable Document Format (PDF) files. The family comprises Acrobat Reader (formerly Reader), Acrobat (former ...
itself as well as
Adobe InDesign Adobe InDesign is a desktop publishing and page layout designing software application produced by Adobe Inc. and first released in 1999. It can be used to create works such as posters, flyers, brochures, magazines, newspapers, presentations, ...
, Adobe FrameMaker,
Adobe Illustrator Adobe Illustrator is a vector graphics editor and design program developed and marketed by Adobe Inc. Originally designed for the Apple Macintosh, development of Adobe Illustrator began in 1985. Along with Creative Cloud (Adobe's shift to m ...
,
Adobe Photoshop Adobe Photoshop is a raster graphics editor developed and published by Adobe Inc. for Windows and macOS. It was originally created in 1988 by Thomas and John Knoll. Since then, the software has become the industry standard not only in r ...
.
Google Google LLC () is an American multinational technology company focusing on search engine technology, online advertising, cloud computing, computer software, quantum computing, e-commerce, artificial intelligence, and consumer electro ...
's online office suite
Google Docs Google Docs is an online word processor included as part of the free, web-based Google Docs Editors suite offered by Google, which also includes: Google Sheets, Google Slides, Google Drawings, Google Forms, Google Sites and Google Keep. Go ...
allows for uploading and saving to PDF. Some web apps offer free PDF editing and annotation tools. The
Free Software Foundation The Free Software Foundation (FSF) is a 501(c)(3) non-profit organization founded by Richard Stallman on October 4, 1985, to support the free software movement, with the organization's preference for software being distributed under copyleft ...
once thought of as one of their high priority projects to be "developing a free, high-quality and fully functional set of libraries and programs that implement the PDF file format and associated technologies to the ISO 32000 standard." In 2011, however, the GNU PDF project was removed from the list of "high priority projects" due to the maturation of the Poppler library, which has enjoyed wider use in applications such as Evince with the
GNOME A gnome is a mythological creature and diminutive spirit in Renaissance magic and alchemy, first introduced by Paracelsus in the 16th century and later adopted by more recent authors including those of modern fantasy literature. Its chara ...
desktop environment. Poppler is based on
Xpdf Xpdf is a free and open-source PDF viewer for operating systems supported by the Qt toolkit. Versions prior to 4.00 were written for the X Window System and Motif. Functions Xpdf runs on nearly any Unix-like operating system. Binaries are a ...
code base. There are also commercial development libraries available as listed in List of PDF software. The Apache PDFBox project of the
Apache Software Foundation The Apache Software Foundation (ASF) is an American nonprofit corporation (classified as a 501(c)(3) organization in the United States) to support a number of open source software projects. The ASF was formed from a group of developers of the A ...
is an open source Java library for working with PDF documents. PDFBox is licensed under the Apache License.


Printing

Raster image processors (RIPs) are used to convert PDF files into a raster format suitable for imaging onto paper and other media in printers, digital production presses and
prepress Prepress is the term used in the Printing and Publishing industries for the processes and procedures that occur between the creation of a print layout and the final printing. The prepress process includes the preparation of artwork for press, medi ...
in a process known as
rasterisation In computer graphics, rasterisation (British English) or rasterization (American English) is the task of taking an image described in a vector graphics format (shapes) and converting it into a raster image (a series of pixels, dots or lines, whi ...
. RIPs capable of processing PDF directly include the Adobe PDF Print Engine from
Adobe Systems Adobe Inc. ( ), originally called Adobe Systems Incorporated, is an American multinational computer software company incorporated in Delaware and headquartered in San Jose, California. It has historically specialized in software for the c ...
and Jaws and the Harlequin RIP from Global Graphics. In 1993, the Jaws raster image processor from Global Graphics became the first shipping prepress RIP that interpreted PDF natively without conversion to another format. The company released an upgrade to their Harlequin RIP with the same capability in 1997.
Agfa-Gevaert Agfa-Gevaert N.V. (Agfa) is a Belgian-German multinational corporation that develops, manufactures, and distributes analogue and digital imaging products, software, and systems. It has three divisions: * Agfa Graphics, which offers integrated pr ...
introduced and shipped Apogee, the first prepress workflow system based on PDF, in 1997. Many commercial offset printers have accepted the submission of press-ready PDF files as a print source, specifically the PDF/X-1a subset and variations of the same. The submission of press-ready PDF files is a replacement for the problematic need for receiving collected native working files. In 2006, PDF was widely accepted as the standard print job format at the
Open Source Development Labs Open Source Development Labs (OSDL) was a non-profit organization supported by a consortium to promote Linux for enterprise computing. Founded in 2000, OSDL positioned itself as an independent, non-profit lab for developers who are adding enterpris ...
Printing Summit. It is supported as a print job format by the
Common Unix Printing System CUPS (formerly an acronym for Common UNIX Printing System) is a modular printing system for Unix-like computer operating systems which allows a computer to act as a print server. A computer running CUPS is a host that can accept print jobs f ...
and desktop application projects such as
GNOME A gnome is a mythological creature and diminutive spirit in Renaissance magic and alchemy, first introduced by Paracelsus in the 16th century and later adopted by more recent authors including those of modern fantasy literature. Its chara ...
, KDE,
Firefox Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements current ...
, Thunderbird,
LibreOffice LibreOffice () is a free and open-source office productivity software suite, a project of The Document Foundation (TDF). It was forked in 2010 from OpenOffice.org, an open-sourced version of the earlier StarOffice. The LibreOffice suite c ...
and
OpenOffice OpenOffice or open office may refer to: Computing Software * OpenOffice.org (OOo), a discontinued open-source office software suite, originally based on StarOffice * Apache OpenOffice (AOO), a derivative of OOo by the Apache Software Foundation, ...
have switched to emit print jobs in PDF. Some desktop printers also support direct PDF printing, which can interpret PDF data without external help.


Native display model

PDF was selected as the "native" metafile format for
Mac OS X macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac (computer), Mac computers. Within the market of ...
, replacing the
PICT The Picts were a group of peoples who lived in what is now northern and eastern Scotland (north of the Firth of Forth) during Late Antiquity and the Early Middle Ages. Where they lived and what their culture was like can be inferred from e ...
format of the earlier
classic Mac OS Mac OS (originally System Software; retronym: Classic Mac OS) is the series of operating systems developed for the Macintosh family of personal computers by Apple Computer from 1984 to 2001, starting with System 1 and ending with Mac OS 9. ...
. The imaging model of the
Quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical fo ...
graphics layer is based on the model common to Display PostScript and PDF, leading to the nickname ''Display PDF''. The Preview application can display PDF files, as can version 2.0 and later of the
Safari A safari (; ) is an overland journey to observe wild animals, especially in eastern or southern Africa. The so-called "Big Five" game animals of Africa – lion, leopard, rhinoceros, elephant, and Cape buffalo – particularly form an ...
web browser. System-level support for PDF allows Mac OS X applications to create PDF documents automatically, provided they support the OS-standard printing architecture. The files are then exported in PDF 1.3 format according to the file header. When taking a screenshot under Mac OS X versions 10.0 through 10.3, the image was also captured as a PDF; later versions save screen captures as a PNG file, though this behavior can be set back to PDF if desired.


Annotation

Adobe Acrobat Adobe Acrobat is a family of application software and Web services developed by Adobe Inc. to view, create, manipulate, print and manage Portable Document Format (PDF) files. The family comprises Acrobat Reader (formerly Reader), Acrobat (former ...
is one example of proprietary software that allows the user to annotate, highlight, and add notes to already created PDF files. One UNIX application available as
free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, ...
(under the
GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for genera ...
) is PDFedit. The
freeware Freeware is software, most often proprietary, that is distributed at no monetary cost to the end user. There is no agreed-upon set of rights, license, or EULA that defines ''freeware'' unambiguously; every publisher defines its own rules for th ...
Foxit Reader, available for Microsoft Windows,
macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...
and
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, wh ...
, allows annotating documents. Tracker Software's PDF-XChange Viewer allows annotations and markups without restrictions in its freeware alternative.
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancesto ...
's
macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...
's integrated PDF viewer, Preview, does also enable annotations as does the open-source software Skim, with the latter supporting interaction with
LaTeX Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well. In nature, latex is found as a milky fluid found in 10% of all flowering plants (angios ...
, SyncTeX, and PDFSync and integration with
BibDesk BibDesk is an open-source reference management software package for macOS, used to manage bibliographies and references when writing essays and articles. It can also be used to organize and maintain a library of documents in PDF format and other ...
reference management software. Freeware
Qiqqa Qiqqa (pronounced "Quicker") is a free and opensource software that allows researchers to work with thousands of PDFs. It combines PDF reference management tools, a citation manager, and a mind map brainstorming tool. It integrates with Micros ...
can create an annotation report that summarizes all the annotations and notes one has made across their library of PDFs. The Text Verification Tool exports differences in documents as annotations and markups. There are also web annotation systems that support annotation in pdf and other documents formats. In cases where PDFs are expected to have all of the functionality of paper documents, ink annotation is required.


Alternatives

The Open XML Paper Specification is a competing format used both as a page description language and as the native print spooler format for Microsoft Windows since
Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, which was released five years before, at the time being the longest time span between successive releases of ...
. Mixed Object: Document Content Architecture is a competing format. MO:DCA-P is a part of Advanced Function Presentation.


See also

* Web document *
XSL Formatting Objects XSL-FO (XSL Formatting Objects) is a markup language for XML document formatting that is most often used to generate PDF files. XSL-FO is part of XSL (Extensible Stylesheet Language), a set of W3C technologies designed for the transformation and ...


References


Further reading

* * PDF 2.0 * PDF 2.0
PDF 1.7 (ISO 32000-1:2008)

PDF 1.7
an
errata to 1.7

PDF 1.6
() an
errata to 1.6

PDF 1.5
an
errata to 1.5

PDF 1.4
() an
errata to 1.4

PDF 1.3
() an
errata to 1.3


External links


PDF Association
– The PDF Association is the industry association for software developers producing or processing PDF files.


Adobe: PostScript vs. PDF
– Official introductory comparison of PS, EPS vs. PDF. * – Information about PDF/E and PDF/UA specification for accessible documents file format (archived by The Wayback Machine)
PDF/A-1 ISO standard
published by the
International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in A ...
(with corrigenda)
PDF Reference and Adobe Extensions to the PDF Specification


– Introduction to PDF vs. PostScript and PDF internals (up to v1.3)
The Camelot Paper
– the paper in which John Warnock outlined the project that created PDF
Everything you wanted to know about PDF but was afraid to ask

recording of a talk by Leonard Rosenthol
(45 mins) (
Adobe Systems Adobe Inc. ( ), originally called Adobe Systems Incorporated, is an American multinational computer software company incorporated in Delaware and headquartered in San Jose, California. It has historically specialized in software for the c ...
) at TUG 2007 {{Authority control Computer-related introductions in 1993 Adobe Inc. Digital press Electronic documents Graphics file formats ISO standards Office document file formats Open formats Page description languages Vector graphics