I haven't looked at the programme Bill D links to, but have recently been playing with a different one which does something similar.

I got PDF Expert 4 (or is it Expert PDF?) on a magazine cover disc. It contains two programmes. One is a virtual printer which allows you instead of printing a hard copy of a file onto paper, creates a PDF file.
The second programe allows some basic editing of PDF files as long as they are not "security locked" by the producer of the document. It allows you to add text, import new bitmap images and draw/edit vector graphics. It is a bit fiddly to use, but is okay for simple changes to a document.
For PDFs which are "locked", it is possible to "print" from Acrobat Reader using the virtual printer, and thereby create a new unlocked PDF. This can change text in the original into a graphic in the new "copy", but did allow me to edit a document I wouldn't otherwise have been able to touch.

The Company is http://shop.avanquest.com/uk/.
Current version is PDF Expert 5 . which will probably become a dead link when they start selling the next version. Version 5 reckons to do a lot more than version 4.
They have downloads for free demo versions of the current product, but I don't know what restrictions they put on them.
They also sell one which converts PDFs into Word document format.

Quack!
Geoff the Duck.