How Does PDF Format Work?by Shawn M. Tomlinson
Professional-level software program files used to be so large that they were unmanageable if it had all its graphics embedded. That is, "part of" the file. The way software developers got around this in, say, QuarkXPress, was to create the central file with invisible links to its graphics or fonts. This made the file smaller and easier to deal. It would print fine, too, as long as those links still were connected. As any QXP designer knows from experience, however, the moment you copy the file somewhere else and forget to take the graphics with you, QXP will print a low-resolution copy of the file.
In the early 1990s, many programs worked this way. That's when Adobe introduced Acrobat with its portable document file format, or PDF. This format changed the way files could be moved around from place to place, and it allowed strict controls to be placed on files, including solidifying them so no one could make changes, presenting them to others exactly as they looked to the designer, and allowing or disallowing printing and copying.
The PDF format essentially gathers all the disparate parts of a file---including fonts and graphics---and embeds them into one file. This makes a larger file than the original, but smaller when you consider the original with all its linked parts as a whole. Since Adobe Reader is distributed free to anyone in both the Windows and Macintosh formats, anyone can view a PDF. Aside from the full Acrobat, some high-level software---such as QuarkXPress from version 6.0 and on, and Photoshop---have built-in PDF-making software.
- photo_camera Adobe Corp.