Portable Document Format (PDF) is a file format developed by Adobe Systems for representing documents in a manner that is independent of the original application software, hardware, and operating system used to create those documents. A PDF file can describe documents containing any combination of text, graphics, and images in a device independent and resolution independent format. These documents can be one page or thousands of pages, very simple or extremely complex with a rich use of fonts, graphics, color, and images. PDF is an open standard, and anyone may write applications that can read or write PDFs royalty-free.
In addition to encapsulating text and graphics, PDF files are most appropriate for encoding the exact look of a document in a device-independent way. In contrast, markup languages such as HTML defer many display decisions to a rendering device such as a browser, and will not look the same on different computers.
Free readers for many platforms are available: the free Adobe Reader by Adobe Systems, the free Foxit Reader [1], and several free open source readers, including Xpdf for POSIX-like systems with the X Window System; KPDF, a viewer based on Xpdf for KDE; GPdf, a derivative of Xpdf for GNOME; Evince, a document viewer for GNOME (fork of GPdf) that can view PDF-files; GSPdf and ViewPDF [2], for GNUstep; and front-ends for many platforms to Ghostscript.
Proper subsets of PDF, collectively called PDF/X, have been standardized by ISO.
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