Before PDF: John Warnock's 'Camelot'
Karl De Abrew writes: "In the Spring of 1991 Dr. John Warnock wrote a paper he
dubbed "Camelot" in which the Adobe Systems Co-founder and
CEO laid out the foundation for what has become Acrobat/PDF.
With the author's permission, Planet PDF is pleased to publish
the full-text of that historic document." Of course, now it's 2002, and the dream of universal display / printing remains only partly realized; PDFs really have helped to narrow the gap between dream and reality, though.
Also while the pdf format is controlled by Adobe, the specs are open and available (contrast this with Microsoft's format which is a complete mystery), you can get the specs from Adobe's site and nothing prevents you from writing code that manipulates pdf files (well yes there are issues with compression algorithm).
This openess is the reason why Apple chose to use pdf as their graphic description language for OS X (older OS versions used QuickDraw). The windows page description language, is, I think, WMF. It's funny to think that the basic page description language used under Unix is Postscript, which is much more closed than PDF.