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Beginning with PDF version 1.5, indirect objects may also be located in special streams known as object streams.
The graphics commands that are output by the Post Script code are collected and tokenized.
Any files, graphics, or fonts to which the document refers also are collected. Therefore, the entire Post Script world (fonts, layout, measurements) remains intact.
At the end of a PDF file is a trailer introduced with the 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.
Unlike Post Script, PDF does not allow a single path to mix text outlines with lines and curves. Strokes and fills can use any color set in the graphics state, including 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.
Adobe Systems made the PDF specification available free of charge in 1993.
In the early years PDF was popular mainly in desktop publishing workflows, and competed with a variety of formats such as Dj Vu, Envoy, Common Ground Digital Paper, Farallon Replica and even Adobe's own Post Script format.
PDF has (as of version 1.6) 24 graphics state properties, of which some of the most important are: As in Post Script, vector graphics 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.
PDF was standardized as an open format, ISO 32000, in 2008, and does not require any royalties for its implementation.