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==Technology==
[[PDF]] is primarily the combination of three technologies:
* a cut-down form of [[PostScript]] for generating the layout and graphics,
* a font-embedding/replacement system to allow fonts to travel with the documents, and
* a structured storage system to bundle these elements into a single file, with data compression where appropriate.

[[PostScript]] is a page description language that is run in an interpreter to generate an image. This process requires a fair amount of resources.

[[PDF]] is a subset of those [[PostScript]] language elements that define the graphics, and only requires a very simple interpreter. For instance, flow control commands like <code>if</code> and <code>loop</code> are removed, while graphics commands such as <code>lineto</code> remain.

That means that the process of turning [[PDF]] back into a graphic is a matter of simply reading the description, rather than running a program in the [[PostScript]] interpreter. However, the entire [[PostScript]] world in terms of fonts, layout and measurement remains intact.

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 the document references are also collected; and finally everything is compressed into a single file.

As a document format, [[PDF]] has several advantages over [[PostScript]]:
* A [[PDF]] document resides in a single file, whereas the same document in [[PostScript]] may span multiple files (graphics, etc.) and probably occupies more space.
* [[PDF]] contains already-interpreted results of the [[PostScript]] source code, so it is less computation-intensive and faster to open, and there is a more direct correspondence between changes to items in the [[PDF]] page description and changes to the resulting appearance of the page.
* [[PDF]] (starting from version 1.4) supports true object transparency while [[PostScript]] does not.
* [[PDF]] allows font embedding to ensure that the "proper" fonts are displayed. While this is possible with [[PostScript]], such files cannot normally be distributed freely because of font licensing agreements.