Well I know from personal experience in feeding PDF's into the iLiad's version of xpdf that they've broken a few things in it already.
The Postscript rendering model, which is the heart of PDF, is for some obtuse and impossible to understand. If you grok (
http://whatis.techtarget.com/definit...212216,00.html) it, you can do wondrous things. If you don't grok it and you wind up fighting with it: Frankenstein.
Pan and Zoom are easy, very easy, they are biscuits and gravy to Postscript. iRex developers need to read the blue book (
http://www-cdf.fnal.gov/offline/Post...0postscript%22) work the examples, read the book again, repeat 3 times.
Then they may find the purple book handy as well (sorry, no freebie from Fermilab here
http://www.amazon.com/Programming-Di...705742?ie=UTF8).
This level of understanding is needed so you don't break people's files when you go hacking around in the guts of xpdf.