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The latest updates adds one unbelievable characteristic, in add-on to the bug holes. Users can now change over the Web page they 're looking at into a PDF, complete with hyperlinks. It does n't wish pages with embedded content, altering Flash pictures, for illustration, into links back to Adobe. But even with that restriction, the former Web page looks all right in as a PDF. The circuit board now supports Firefox 3 and its societal networking subdivision, Flock. PDF Download is n't fancy for an extension that measures itself as `` one of the most popular Firefox additions of all time, '' but it could be a large aid for journalists, authorities workers, and others who spend considerable clip with PDFs.

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History and standardisation

PDF was developed in the early 1990s as a manner to portion computing machine paperss, including text data format and inline images. It was among a figure of viing formats such as DjVu, Envoy, Common Ground Digital Paper, Farallon Replica and even Adobe 's ain PostScript format. In those early old ages before the rise of the World Wide Web and HTML paperss, PDF was popular chiefly in desktop publication work flows. Adobe Systems made the PDF specification available free of charge in 1993. PDF was a proprietary format controlled by Adobe, until it was officially released as an unfastened criterion on July 1, 2008, and published by the International Organization for Standardization as ISO 32000-1:2008, at which clip control of the specification passed to an ISO Committee of voluntary industry experts. In 2008, Adobe published a Public Patent License to ISO 32000-1 allowing royalty-free rights for all patents owned by Adobe that are necessary to do, utilize, sell, and administer PDF compliant executions.

However, there are still some proprietary engineerings defined merely by Adobe, such as Adobe XML Forms Architecture ( XFA ) and JavaScript extension for Acrobat, which are referenced by ISO 32000-1 as normative and indispensable for the application of the ISO 32000-1 specification. These proprietary engineerings are non standardized and their specification is published merely on Adobe’s web site. Many of them are besides non supported by popular third-party executions of PDF. So when organisations publish PDFs which use these proprietary engineerings, they present handiness issues for some users.

File construction

Objects may be either direct ( embedded in another object ) or indirect. Indirect objects are numbered with an object figure and a coevals figure and defined between the obj and endobj keywords. An index tabular array, besides called the cross-index tabular array and marked with the xref keyword, follows the chief organic structure and gives the byte beginning of each indirect object from the start of the file. This design allows for efficient random entree to the objects in the file, and besides allows for little alterations to be made without rewriting the full file ( incremental update ) . Get downing with PDF version 1.5, indirect objects may besides be located in particular watercourses known as object watercourse. This technique reduces the size of files that have big Numberss of little indirect objects and is particularly utile for Tagged PDF.

There are two layouts to the PDF files: non-linear ( non `` optimized '' ) and additive ( `` optimized '' ) . Non-linear PDF files consume less disk infinite than their additive opposite numbers, though they are slower to entree because parts of the information required to assemble pages of the papers are scattered throughout the PDF file. Linear PDF files ( besides called `` optimized '' or `` web optimized '' PDF files ) are constructed in a mode that enables them to be read in a Web browser plugin without waiting for the full file to download, since they are written to harrow in a additive ( as in page order ) manner. PDF files may be optimized utilizing Adobe Acrobat package or QPDF.

Imaging theoretical account

Within text strings, characters are shown utilizing character codifications ( whole numbers ) that map to glyphs in the current fount utilizing an encryption. There are a figure of predefined encryptions, including WinAnsi, MacRoman, and a big figure of encryptions for East Asiatic linguistic communications, and a fount can hold its ain constitutional encryption. ( Although the WinAnsi and MacRoman encryptions are derived from the historical belongingss of the Windows and Macintosh runing systems, founts utilizing these encryptions work every bit good on any platform. ) PDF can stipulate a predefined encryption to utilize, the fount 's constitutional encryption or supply a search tabular array of differences to a predefined or constitutional encryption ( non recommended with TrueType founts ) . The encoding mechanisms in PDF were designed for Type 1 founts, and the regulations for using them to TrueType founts are complex.

The original imagination theoretical account of PDF was, like PostScript 's, opaque: each object drawn on the page wholly replaced anything antecedently marked in the same location. In PDF 1.4 the imagination theoretical account was extended to let transparence. When transparence is used, new objects interact with antecedently marked objects to bring forth blending effects. The add-on of transparence to PDF was done by agencies of new extensions that were designed to be ignored in merchandises written to the PDF 1.3 and earlier specifications. As a consequence, files that use a little sum of transparence might see tolerably in older viewing audiences, but files doing extended usage of transparence could be viewed falsely in an older spectator without warning.

Synergistic elements

Rich Media PDF is a term that is used to depict synergistic content that can be embedded or linked to inside of a PDF. This content must be produced utilizing the Flash file format. When Adobe bought Macromedia, the gem of the company was Flash, and the Flash participant was embedded indoors Adobe Acrobat and Adobe Reader, taking the demand for third-party circuit boards such as Flash, QuickTime, or Windows Media. Unfortunately, this caused a rift with Apple as QuickTime picture was prohibited from PDF. Rich Media expert Robert Connolly believes this event triggered the war between Apple and Adobe over the Flash iPhone/iPad difference. Rich Media PDF will non run in Apple 's iOS devices such as the iPad, and interactivity is limited.

The Forms Data Format ( FDF ) is based on PDF, it uses the same sentence structure and has basically the same file construction, but is much simpler than PDF, since the organic structure of an FDF papers consists of merely one required object. Forms Data Format is defined in the PDF specification ( since PDF 1.2 ) . The Forms Data Format can be used when subjecting signifier informations to a waiter, having the response, and integrating into the synergistic signifier. It can besides be used to export signifier informations to stand-alone files that can be imported back into the corresponding PDF synergistic signifier. Get downing in PDF 1.3, FDF can be used to specify a container for notes that are separate from the PDF papers they apply to. FDF typically encapsulates information such as X.509 certifications, petitions for certifications, directory scenes, timestamp waiter scenes, and embedded PDF files for web transmittal. The FDF uses the MIME content type application/vnd.fdf, file name extension.fdf and on Mac OS it uses file type 'FDF ' . Support for importing and exporting FDF stand-alone files is non widely implemented in free or freeware PDF package. For illustration, there is no import/export support in Evince, Okular, Poppler, KPDF or Sumatra PDF, nevertheless, Evince, Okular and Poppler support make fulling in of PDF Acroforms and salvaging filled informations inside the PDF file. Import support for stand-alone FDF files is implemented in Adobe Reader ; export and import support ( including economy of FDF informations in PDF ) is for illustration implemented in Foxit Reader and PDF-XChange Viewer Free ; salvaging of FDF informations in a PDF file is besides supported in pdftk.

XML Forms Data Format ( XFDF ) is the XML version of Forms Data Format, but the XFDF implements merely a subset of FDF incorporating signifiers and notes. There are non XFDF equivalents for some entries in the FDF dictionary - such as the Status, Encoding, JavaScript, Pages keys, EmbeddedFDFs, Differences and Target. In add-on, XFDF does non let the spawning, or add-on, of new pages based on the given informations ; as can be done when utilizing an FDF file. The XFDF specification is referenced ( but non included ) in PDF 1.5 specification ( and in ulterior versions ) . It is described individually in XML Forms Data Format Specification. The PDF 1.4 specification allowed form entries in XML format, but this was replaced by entries in XFDF format in the PDF 1.5 specification. XFDF conforms to the XML criterion.

XFDF can be used the same manner as FDF ; e.g. , signifier informations is submitted to a waiter, alterations are made, so sent back and the new signifier informations is imported in an synergistic signifier. It can besides be used to export signifier informations to stand-alone files that can be imported back into the corresponding PDF synergistic signifier. A support for importing and exporting XFDF stand-alone files is non widely implemented in free or freeware PDF package. Import of XFDF is implemented in Adobe Reader 5 and ulterior versions ; import and export is implemented in PDF-XChange Viewer Free ; implanting of XFDF informations in PDF signifier is implemented in pdftk ( pdf toolkit ) .

In the PDF 1.5 format, Adobe Systems introduced a new, proprietary format for signifiers, viz. Adobe XML Forms Architecture ( XFA ) signifiers. The XFA 2.02 is referenced in the PDF 1.5 specification ( and besides in ulterior versions ) but is described individually in Adobe XML Forms Architecture ( XFA ) Specification, which has several versions. XFA specification is non included in ISO 32000-1 PDF 1.7 and is merely referenced as an external proprietary specification created by Adobe. XFA was non standardized as an ISO criterion. In 2011 the ISO Committee ( TC 171/SC 2/WG 8 ) urged Adobe Systems to subject the XFA Specification for standardisation.

XFA signifiers can be created and used as PDF files or as XDP ( XML Data Package ) files. The format of an XFA resource in PDF is described by the XML Data Package Specification. The XDP may be a standalone papers or it may in bend be carried inside a PDF papers. XDP provides a mechanism for boxing signifier constituents within a environing XML container. An XDP can besides box a PDF file, along with XML signifier and templet informations. PDF may incorporate XFA ( in XDP format ) , but besides XFA may incorporate PDF. When the XFA ( XML Forms Architecture ) grammars used for an XFA signifier are moved from one application to another, they must be packaged as an XML Data Package.

Get downing with PDF 1.5, the text contents of variable text signifier Fieldss, every bit good as markup notes may include arranging information ( manner information ) . These rich text strings are XML paperss that conform to the rich text conventions specified for the XML Forms Architecture specification 2.02, which is itself a subset of the XHTML 1.0 specification, augmented with a restricted set of CSS2 manner properties. In PDF 1.6, PDF supports the rich text elements and properties specified in the XML Forms Architecture ( XFA ) Specification, 2.2. In PDF 1.7, PDF supports the rich text elements and properties specified in the XML Forms Architecture ( XFA ) Specification, 2.4.

Most PDF processors do non manage XFA content. When bring forthing a shell PDF it is recommended to include in the PDF markup a simple one-page PDF image exposing a warning message ( e.g. `` To see the full contents of this papers, you need a ulterior version of the PDF spectator. `` , etc. ) . PDF processors that can render XFA content should either non expose the supplied warning page image or replace it rapidly with the dynamic signifier content. Examples of PDF package with some support of XFA rendering include Adobe Reader for Windows, Linux, macOS ( but non Adobe Reader Mobile for Android or Io ) or Nuance PDF Reader.

Security and signatures

The standard security provided by Acrobat PDF consists of two different methods and two different watchwords, user watchword, which encrypts the file and prevents gap, and proprietor watchword, which specifies operations that should be restricted even when the papers is decrypted, which can include: printing, copying text and artworks out of the papers, modifying the papers, or adding or modifying text notes and AcroForm Fieldss. The user watchword ( controls opening ) encrypts the file and requires password checking to get the better of, with trouble depending on watchword strength and encoding method – it is potentially really unafraid ( presuming good watchword and encoding method without known onslaughts ) . The proprietor watchword ( controls operations ) does non code the file, and alternatively relies on client package to esteem these limitations, and is non unafraid. An `` proprietor watchword '' can be removed by many normally available `` PDF snap '' package, including some free online services. Therefore, the usage limitations that a papers writer topographic points on a PDF papers are non unafraid, and can non be assured once the file is distributed ; this warning is displayed when using such limitations utilizing Adobe Acrobat package to make or redact PDF files.


PDF files can be created specifically to be accessible for handicapped people. PDF file formats in usage as of 2014 can include tickets ( XML ) , text equivalents, captions, audio descriptions, etc. Tagged PDF is required in the PDF/A-1a specification. Some package can automatically bring forth labeled PDFs, but this characteristic is non ever enabled by default. Leading screen readers, including JAWS, Window-Eyes, Hal, and Kurzweil 1000 and 3000 can read tagged PDFs out loud, as can later versions of the Acrobat and Acrobat Reader plans. Furthermore, tagged PDFs can be re-flowed and magnified for readers with ocular damages. Problems remain with adding tickets to older PDFs and those that are generated from scanned paperss. In these instances, handiness tickets and re-flowing are unavailable, and must be created either manually or with OCR techniques. These procedures are unaccessible to some handicapped people.

One of the important challenges with PDF handiness is that PDF paperss have three distinguishable positions, which, depending on the papers 's creative activity, can be inconsistent with each other. The three positions are ( I ) the physical position, ( two ) the tags position, and ( three ) the content position. The physical position is displayed and printed ( what most people consider a PDF papers ) . The tags position is what screen readers and other assistive engineerings use to present a high-quality pilotage and reading experience to users with disablements. The content position is based on the physical order of objects within the PDF 's content watercourse and may be displayed by package that does non to the full back up the tickets position, such as the Reflow characteristic in Adobe 's Reader.

Viruss and feats

From clip to clip, new exposures are discovered in assorted versions of Adobe Reader, motivating the company to publish security holes. Other PDF readers are besides susceptible. One worsening factor is that a PDF reader can be configured to get down automatically if a web page has an embedded PDF file, supplying a vector for onslaught. If a malicious web page contains an septic PDF file that takes advantage of a exposure in the PDF reader, the system may be compromised even if the browser is unafraid. Some of these exposures are a consequence of the PDF criterion leting PDF paperss to be scripted with JavaScript. Disabling JavaScript executing in the PDF reader can assist extenuate such future feats, although it does non protect against feats in other parts of the PDF screening package. Security experts say that JavaScript is non indispensable for a PDF reader, and that the security benefit that comes from disenabling JavaScript outweighs any compatibility issues caused. One manner of avoiding PDF file feats is to hold a local or web service convert files to another format before sing.

Use limitations and monitoring

Through its LiveCycle Policy Server merchandise, Adobe provides a method to put security policies on specific paperss. This can include necessitating a user to authenticate and restricting the period during which a papers can be accessed or sum of clip a papers can be opened while offline. Once a PDF papers is tied to a policy waiter and a specific policy, that policy can be changed or revoked by the proprietor. This controls paperss that are otherwise `` in the natural state. '' Each papers unfastened and close event can besides be tracked by the policy waiter. Policy waiters can be set up in private or Adobe offers a public service through Adobe Online Services. As with other signifiers of DRM, attachment to these policies and limitations may or may non be enforced by the reader package being used.


Adobe Acrobat is one illustration of proprietary package that allows the user to footnote, high spot, and add notes to already created PDF files. One UNIX application available as free package ( under the GNU General Public License ) is PDFedit. Another GPL-licensed application indigen to the unix environment is Xournal. Xournal allows for footnoting in different founts and colorss, every bit good as a regulation for rapidly underscoring and foregrounding lines of text or paragraphs. Xournal besides has a form acknowledgment tool for squares, rectangles and circles. In Xournal notes may be moved, copied and pasted. The freeware Foxit Reader, available for Microsoft Windows, macOS and Linux, allows footnoting paperss. Tracker Software 's PDF-XChange Viewer allows notes and markups without limitations in its freeware alternate. Apple 's macOS 's incorporate PDF spectator, Preview, does besides enable notes as does the freeware Skim, with the latter back uping interaction with LaTeX, SyncTeX, and PDFSync and integrating with BibDesk mention direction package. Freeware Qiqqa can make an note study that summarizes all the notes and notes one has made across their library of PDFs.


PDF was selected as the `` native '' metafile format for Mac OS X, replacing the PICT format of the earlier authoritative Mac OS. The imaging theoretical account of the Quartz artworks bed is based on the theoretical account common to Display PostScript and PDF, taking to the nickname Display PDF. The Preview application can expose PDF files, as can version 2.0 and subsequently of the Safari web browser. System-level support for PDF allows Mac OS X applications to make PDF paperss automatically, provided they support the OS-standard printing architecture. The files are so exported in PDF 1.3 format harmonizing to the file heading. When taking a screenshot under Mac OS X versions 10.0 through 10.3, the image was besides captured as a PDF ; ulterior versions save screen gaining controls as a PNG file, though this behavior can be set back to PDF if desired.

The Free Software Foundation one time considered one of their high precedence undertakings to be `` developing a free, high-quality and to the full functional set of libraries and plans that implement the PDF file format and associated engineerings to the ISO 32000 criterion. '' In 2011, nevertheless, the GNU PDF undertaking was removed from the list of `` high precedence undertakings '' due to the ripening of the Poppler library, which has enjoyed wider usage in applications such as Evince with the GNOME desktop environment. Poppler is based on Xpdf codification base. There are besides commercial development libraries available as listed in List of PDF package.

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