True Type fonts disappearing when editing in trial version

I'm trying out a trial version of Adobe because I need two things: 1) a way to edit pdfs obviously, and 2) a way to insert live links into pdfs. So far the trial is great!

However, I ran into a problem while editing a pretty text heavy 13 page document. The document had been made originally in iweb. I had no problem editing the first 10 pages, but the last 3 have taken 3 days. Random text disapears after about 3 minutes of editing. I've gone through and changed the fonts to a true type (first Arial) which seemed to helped, but just when I had only a paragraph left to go, the problem started happening again. So I started to change everything to Helvetica. Same thing: almost done and disappearing text again. I'm afraid I won't be able to finish the document, but I'm so close! ugh!

I just need to get this document fixed and I can retype it from scratch at a later date, but a deadline looms (actually, I've already missed it).

Any ideas on how to fix this problem?