PDF

PDF, universally readable format for electronic documents. PDF files (generally called PDFs) are widely used because documents converted into PDFs retain all their features, regardless of the application originally used to create them. PDFs can be viewed on any operating system with a PDF-viewer program (which is usually free); thus, PDFs are a valuable medium for mass communication.

The PDF is the result of the Camelot Project, an initiative begun by Adobe Inc. cofounder John Warnock in 1990 to “capture documents from any application, send electronic versions of these documents anywhere, and view and print these documents on any machine.” To realize this ambition, Warnock and his team had to create a new very small file type that could faithfully recreate the content of any source document, and they had to invent the software to create the file.

The Camelot group accomplished this goal by adapting two previous Adobe products: the design software Illustrator and the page-description language PostScript. Illustrator ran on both Microsoft Windows and Apple computers, making it an appropriate foundation on which to base a project that aimed for universal applicability. The PostScript language had already proven itself in desktop publishing by running on Apple’s laser printers.

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Warnock’s team created the new file type by simplifying the PostScript language to its declarative components—that is, the parts of the language that generated a page’s layout and graphics. This pared-down code was combined with a font-embedding system, in which the file carried the fonts used in any source document so that those fonts could be reproduced wherever the file was opened. When possible, data was compressed to shorten the file’s transfer and download times.

The Camelot production team officially released the PDF and its associated suite of programs, collectively known as Adobe Acrobat, on June 15, 1993. At the time, Adobe Acrobat included three separate pieces of software: Acrobat Exchange (later Acrobat) for creating PDFs, Acrobat Reader (later Adobe Reader) for viewing them, and Acrobat Distiller for converting PostScript files into PDFs. Initial public response was tepid. PDFs were slower to download and render than text files with the computers and Internet connections of that time. PDFs also supported only text, images, and hypertext linking to other places within the same document. Adobe Acrobat was expensive; Reader alone cost $50 per user, while personal-use versions of Exchange and Distiller cost $195 and $695, respectively.

Nevertheless, Adobe not only continued to market the software but also further developed it. In addition to improving the mainstream product by adding support for hyperlinks to external sources, interactive elements (such as buttons and checkboxes), and the embedding of audiovisual media, Adobe worked with various organizations, including the International Organization for Standardization (ISO), to create specialized versions of the PDF appropriate for use in specific industries. Generally, these customized PDFs either lack certain features of the primary product or mandate the use of others. PDF/A, for example, is a version of the PDF authorized for use in the archiving industry. The special file type forbids the embedding of audio and video content while requiring standards-based metadata.

Adobe made two major decisions that vastly increased PDF usage. First, in 1994 Adobe gave away its PDF-viewer program, Acrobat Reader, as freeware. This move gave nearly everyone the ability to read PDFs, rapidly expanding consumers’ familiarity with the file type. Second, Adobe struck a deal with Apple to make PDF its default document format on new operating systems, starting in 2001 with Mac OS X. PDF thus became the de facto standard for electronic documentation within less than a decade.

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PDF’s worldwide popularity made its standardization an industry-wide concern. On July 1, 2008, Adobe released the specifications for PDF 1.7 as an open standard. The document was jointly copyrighted by Adobe and ISO. Adobe also gave a public patent license to ISO, providing it royalty-free rights for all Adobe patents necessary to use PDFs. Post-PDF-1.7 development of the format continued under the purview of an ISO committee, and in December 2020 the committee published its work on a second edition of PDF 2.0.