%PDF
| owner = Adobe Systems
| released =
| latest release version = 1.7
| latest release date =
| genre =
| container for =
| contained by =
| extended from =
| extended to =
| standard = ISO/IEC 32000-1:2008
| free =
| url = Adobe PDF Reference Archives
}}
Portable Document Format (PDF) is an open standard for document exchange. The file format created by Adobe Systems in 1993 is used for representing two-dimensional documents in a manner independent of the application software, hardware, and operating system.
Each PDF file encapsulates a complete description of a fixed-layout 2D document that includes the text, fonts, images, and 2D vector graphics which compose the documents. Lately, 3D drawings can be embedded in PDF documents with Acrobat 3D using U3D or PRC and various other data formats. that evolved into the Portable Document Format (PDF).
Originally a proprietary format, PDF was officially released as an open standard on July 1, 2008, and published by the International Organization for Standardization as ISO/IEC 32000-1:2008. Adobe Acrobat, Adobe's suite for reading and creating PDF files, was not freely available; early versions of PDF had no support for external hyperlinks, reducing its usefulness on the Internet; the larger size of a PDF document compared to plain text required longer download times over the slower modems common at the time; and rendering PDF files was slow on the less powerful machines of the day. Additionally, there were competing formats such as Envoy, Common Ground Digital Paper, Farallon Replica and even Adobe's own PostScript format (.ps); in those early years, PDF was popular mainly in desktop publishing workflows. In 1995, AT&T; Labs commenced work on another electronic document standard targeted at libraries and archives for preserving their books and documents, DjVu. This standard has evolved into the .djv/ .djvu format, which has had growing success and penetration in the online world for eBooks, catalogs, and image-sharing.
Adobe soon started distributing its Acrobat Reader (now Adobe Reader) program at no cost, and continued supporting the original PDF, which eventually became the de facto standard for printable documents on the web (a standard web document).
The PDF specification has changed several times and continues to evolve as new versions of Adobe Acrobat are released. There have been nine versions of PDF with corresponding Acrobat releases:
The ISO 32000-1:2008 PDF open standard was published by the ISO on July 1, 2008. PDF is now a published ISO standard, titled Document management—Portable document format—Part 1: PDF 1.7
According to the ISO PDF standard abstract:
ISO 32000-1:2008 specifies a digital form for representing electronic documents to enable users to exchange and view electronic documents independent of the environment in which they were created or the environment in which they are viewed or printed. It is intended for the developer of software that creates PDF files (conforming writers), software that reads existing PDF files and interprets their contents for display and interaction (conforming readers) and PDF products that read and/or write PDF files for a variety of other purposes (conforming products).
A new version named "PDF 2.0" is currently under development (ISO/NP 32000-2 - Document management—Portable document format—Part 2: PDF 2.0).
The PDF combines three technologies:
if and loop are removed, while graphics commands such as lineto remain.
Often, 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:
Objects may be either direct (embedded in another object) or indirect. Indirect objects are numbered with an object number and a generation number. An index table called the xref table gives the byte offset of each indirect object from the start of the file. This design allows for efficient random access to the objects in the file, and also allows for small changes to be made without rewriting the entire file (incremental update). Beginning with PDF version 1.5, indirect objects may also be located in special streams known as object streams. This technique reduces the size of files that have large numbers of small indirect objects and is especially useful for Tagged PDF.
There are two layouts to the PDF files—non-linear (not "optimized") and linear ("optimized"). Non-linear PDF files consume less disk space 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. Linear 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 they are written to disk in a linear (as in page order) fashion. PDF files may be optimized using Adobe Acrobat software or QPDF.
PDF graphics use a device independent Cartesian coordinate system to describe the surface of a page. A PDF page description can use a matrix to scale, rotate, or skew 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 1.6) 24 graphics state properties, of which some of the most important are:
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 pattern of which the simplest are the axial shade (Type 2) and radial shade (Type 3).
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 and PDF/X, prohibit these techniques.
Raster images can be exported using applications such as pdfimages from the xpdf/poppler package, or using the "Export All Images" function in the "Advanced" menu of Adobe Acrobat, version 6 or later.
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.
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 version 9. The blend modes were based on those used by Adobe Photoshop 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.
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 PDF specification:
Alongside the standard PDF action types, Interactive forms (AcroForms) support submitting, resetting, and importing data. 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): 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.
The Forms Data Format (FDF) is based on PDF, it 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 PDF format specification (since PDF 1.2). The Forms Data Format can be used when submitting form data to a server, receiving the response, and incorporating 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. Beginning in PDF 1.3, FDF can be used to define a container for annotations that are separate from the PDF document to which they apply. FDF is typically used to encapsulate information such as X.509 certificates, requests for certificates, directory settings, timestamp server settings, and embedded PDF files for network transmission.
XML Forms Data Format (XFDF) is the XML version of Forms Data Format, but the XFDF implements only a subset of FDF containing forms and annotations. There are not XFDF equivalents for some entries in the FDF dictionary - such as the Status, Encoding, JavaScript, Pages keys, EmbeddedFDFs, Differences and Target. 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 Adobe XFA Forms are not compatible with AcroForms. Creating XFA Forms for use in Adobe Reader requires Adobe LiveCycle Forms Designer. Adobe Reader contains "disabled features" for use of XFA Forms, that will activate only when opening a PDF document that was created using enabling technology available only from Adobe. The XFA Forms are not compatible with Adobe Reader prior to version 6.
When the PDF and XFA are combined, the result is a form in which each page of the XFA form overlays a PDF background. This architecture is sometimes referred to as XFAF (XFA Foreground). The alternative is to express all of the form, including boilerplate, directly in XFA. It is sometimes called full XFA. and thus these restrictions are obviously ineffective in letting the author control what can and cannot be done with the pdf file he or she created, once it is distributed. This warning is also displayed when applying such restrictions using Adobe Acrobat software to create or edit PDF files.
Even without removing the password, most freeware or open source PDF readers will ignore the digital rights management "protections" and will allow the user to print or make copy of excerpts of the text as if the document were not limited by password protection.
Later, in PDF 1.4, support was added for the Metadata Streams, using the Extensible Metadata Platform (XMP) to add XML standards-based extensible metadata as used in other file formats. This allows metadata to be attached to any stream in the document, such as information about embedded illustrations, as well as the whole document (attaching to the document catalog), using an extensible schema.
A PDF/H variant (PDF for Healthcare) is being developed. However, it may consist more of a set of "best practices" than of a specific format or subset.
Adobe is exploring an XML-based next-generation PDF code named Mars. Information about the Mars file format is published by Adobe at http://www.adobe.com/go/mars and also http://labs.adobe.com/wiki/index.php/Mars.
The format of graphic elements of Mars is sometimes described simply as "SVG", but according to the version 0.8 draft specification of November 2007 (§3 Mars SVG Support) the format is actually merely similar to SVG: it contains both additions to and subtractions from SVG, so it is in general neither viewable by nor creatable with standard SVG tools: some things will look noticeably different between SVG viewers and Mars viewers.
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 read (useful for people with poor eyesight). The content view is displayed when the document is re-flowed to Acrobat (useful for people with mobility disability). For a PDF document to be accessible, the three views must be consistent with each other.
From time to time, new vulnerabilities are discovered in various versions of Adobe Reader, prompting the company to issue security fixes. One aggravating factor is that Adobe Reader is by default integrated into browsers, and can be started automatically if the web page has an embedded PDF file, opening up a new vector of attack. If a malicious web page contains an infected PDF file that takes advantage of some vulnerability in Adobe Reader, the system is compromised even if the browser is up-to-date.
On March 30, 2010 security researcher Didier Stevens reported an "exploit" that causes an arbitrary executable to be run when a PDF file is opened, after the user accepts a warning prompt. The exploit works in several different PDF viewers including Adobe Reader and Foxit Reader.
PDF files may also contain embedded DRM restrictions that provide further controls that limit copying, editing or printing. The restrictions on copying, editing, or printing depend on the reader software to obey them, so the security they provide is limited.
The PDF Reference has technical details or see for an end-user overview. Like HTML files, PDF files may submit information to a web server. This could be used to track the IP address of the client PC, a process known as phoning home. After update 7.0.5 to Acrobat Reader, the user will be notified "via a dialogue box that the author of the file is auditing usage of the file, and be offered the option of continuing."
Through its LiveCycle Policy Server product, Adobe provides a method to set security policies on specific documents. This can include requiring a user to authenticate and limiting the timeframe a document can be accessed or amount of time a document can be opened while offline. Once a PDF document is tied to a policy server and a specific policy, that policy can be changed or revoked by the owner. This controls documents that are otherwise "in the wild." Each document open and close event can also be tracked by the policy server. Policy servers can be set up privately or Adobe offers a public service through Adobe Online Services.
Such features are not omissions from PDF, whose scope only covers electronic documents. The JDF standard covers such aspects; however, it is a complex standard, which is not widely implemented. This hinders the replacement of PostScript by PDF.
In later PDF revisions, a PDF document can also support links (inside document or web page), forms, JavaScript (initially available as plugin for Acrobat 3.0), or any other types of embedded contents that can be handled using plug-ins.
PDF 1.6 supports interactive 3D documents embedded in the PDF - 3D drawings can be embedded using U3D or PRC and various other data formats.
Two PDF files that look similar on a computer screen may be of very different sizes. For example, a high resolution raster image takes more space than a low resolution one. Typically higher resolution is needed for printing documents than for displaying them on screen. Other things that may increase the size of a file is embedding full fonts, especially for Asiatic scripts, and storing text as graphics.
See List of PDF software for a more complete list of PDF editors.
There are also web annotation systems which allow to annotate pdf and other documents formats, e.g. A.nnotate, crocodoc, WebNotes.
In cases where PDFs are expected to have all of the functionality of paper documents, ink annotation is required. Many programs which accept ink input from the mouse are not responsive enough for handwriting using an input tablet or tablet PC. Existing solutions on the PC include Bluebeam PDF Revu, and PDF Annotator.
In 1993 the Jaws RIP 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 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 are a replacement for the problematic need for receiving collected native working files.
PDF was selected as the "native" metafile format for Mac OS X, replacing the PICT format of the earlier Mac OS. The imaging model of the Quartz 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 web browser. System-level support for PDF allows Mac OS X applications to create PDF documents automatically, provided they support the Print command. 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; in 10.4 and 10.5 the default behaviour is set to capture as a PNG file, though this behaviour can be set back to PDF if required.
Some desktop printers also support direct PDF printing, which can interpret PDF data without external help. Currently, all PDF capable printers also support PostScript, but most PostScript printers do not support direct PDF printing.
The Free Software Foundation considers 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." The GNUpdf library has, however, not been released yet, while Poppler has enjoyed wider use in applications such as Evince, which comes with the GNOME desktop environment, at the expense of relying on the GPLv2-licensed Xpdf code base that can't be used by GPLv3 programs. There are also commercial development libraries available as listed in List of PDF software.
The Apache PDFBox project of the Apache Software Foundation is an open source Java library for working with PDF documents. PDFBox is licensed under the Apache License.
Category:Adobe Systems Category:Graphics file formats Category:Open formats Category:Page description languages Category:Vector graphics Category:Computer file formats Category:Digital press Category:ISO standards Category:IEC standards
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![Crewe railway station was completed in 1837 and is one of the most historic railway stations in the world. Built in fields near to Crewe Hall, it originally served the village of Crewe with a population (c. 1831) of just 70 residents.[1] Crewe was chosen after Winsford, seven miles to the north, had rejected an earlier proposal, as had local landowners in neighbouring Nantwich, four miles away.](http://web.archive.org./web/20101210142633im_/http://cdn.wn.com/pd/f5/75/2f7316d686678d29be090cccf821_grande.jpg "Crewe railway station was completed in 1837 and is one of the most historic railway stations in the world. Built in fields near to Crewe Hall, it originally served the village of Crewe with a population (c. 1831) of just 70 residents.[1] Crewe was chosen after Winsford, seven miles to the north, had rejected an earlier proposal, as had local landowners in neighbouring Nantwich, four miles away.")
![Crewe railway station was completed in 1837 and is one of the most historic railway stations in the world. Built in fields near to Crewe Hall, it originally served the village of Crewe with a population (c. 1831) of just 70 residents.[1] Crewe was chosen after Winsford, seven miles to the north, had rejected an earlier proposal, as had local landowners in neighbouring Nantwich, four miles away.](http://web.archive.org./web/20101210142633im_/http://cdn.wn.com/pd/f5/75/2f7316d686678d29be090cccf821_thumb.jpg "Crewe railway station was completed in 1837 and is one of the most historic railway stations in the world. Built in fields near to Crewe Hall, it originally served the village of Crewe with a population (c. 1831) of just 70 residents.[1] Crewe was chosen after Winsford, seven miles to the north, had rejected an earlier proposal, as had local landowners in neighbouring Nantwich, four miles away.")
