I'm making a PDF reader and it works pretty good with most PDFs. While testing with a bunch of different documents (on an iPad), I've found one that crashes the app - it makes heavy use of vector graphics and images so I'm not surprised. I also bought a bunch of PDF readers (most notably Good Reader and ReaddleDocs) to test them with this document, and they all freeze for three or four seconds and then crash.
Now the problem: I just tried it on iBooks and it works flawlessly. How's this possible? Maybe Apple doesn't use the CGPDF set of functions like all other apps do? Or maybe there's something I don't know, like some open source PDF rendering library that could be used instead? (I couldn't find any).
Update: I ended up re-exporting the PDF and now it works fine, but I'll still like to know why iBooks can handle the old one perfectly. :)