Acrobat is NOT a word processor in any way shape or form. Acrobat is intended as a tool for developing digital documents, which can include some small multimedia functionality (playing sounds, playing movies) as well as some forms processing (like an online order form), some low end data processing (like a javascript calculator), document archival (including online OCR of scanned documents).
So one question might be, why do I need Acrobat if I have Word? A partial answer is simply that the Acrobat Reader app is universally standard, so virtually anyone can read a PDF. Sure, there are free Word readers, but it's not the same.
Also, Acrobat is a development tool for any PDF created from any program, so you can do page layout in InDesign, output a PDF and mark it up with hyperlinks to web pages, paste in QuickTimes movies, etc. Word does not give you anywhere near the capability of layout as Indesign or Quark, though Word is quite capable on its own of importing movies and using hyperlinks.
Acrobat is in kind of a limbo right now because some of its intentions have been superceded by programs like Flash, which now handles forms processing and other internet-related tasks much better.
The main niche for Acrobat is document archival, digital document presentation (technical manuals, etc.) and digital proofing (send a PDF to a client of a page design, they can mark it up with comments using Acrobat) and finally digital print document submission to print houses (a Press Quality, in theory, should be printable by anybody. In practice, it falls a bit short, but Acrobat 6 is supposed to have more help in this area).
My question to you is, why do you think you need Acrobat? I'm not being sarcastic, just curious. I understand you want to edit some PDF files, but is that going to be an ongoing thing, or just one of those things that is a one time need? Which makes me wonder, why the heck do you need to edit a PDF? That's an unusual thing to do unless you're a printer. Typically, you would want to edit the master file (Word, Quark, inDesign, etc.) and re-export the PDF, not edit the PDF itself.