I'm pretty sure there isn't much editing you can really do to a PDF. It's sort of the last step before printing, so a lot of the formatting, fonts, layout, etc. are fixed, and not easy to change. Acrobat will let you do some editing (deleting words, inserting text, and some other minor stuff), but it is very limited - you can't insert new line breaks or anything, for example.
If all you have is a PDF, and you want to edit it, then you may be out of luck (unless there are other options I am unaware of - as ranger_nemo mentioned, you can convert it to ASCII, but you're likely to lose something in the translation). However, if you have an ASCII or .tex or some other version of the same document, you can edit that and convert it to PDF when you are done.
Hope this helps