Just an FYI.
I scanned pages from a book I'm reading into pdf files. The built in pdf viewer would not open them (out of memory error.)
Xournal opens them with no problems! And I can highlight the page as a book marker.
Worth mentioning is that the "Annotate PDF" feature displays the pdf in low-resolution at first, but gets more defined after a short delay. This is a great feature because it allows me to start reading right away and the image slowly gets better.

It's also a great note taking application which it what it was designed for.

My only minor complaint is the up/down left/right keys do not scroll the page.

This is definately a thumbs up application!