The PDF format by definition does not allow you to make changes to the file. If you happen to have the Pro Version of Adobe's Acrobat software you can start to edit.
One POSSIBLE solution is to see if you can select portions of the document and cut and paste to a WORD document. If you try to select an area and you get the whole form, you are pretty much out of luck.. then you need to go back to Daves suggestion of finding it on another forum that DOES allow for changes.
Also, you may try this tutorial about how to convert PDF files to Word (doc)
. Once they're converted, you can open the files Microsoft Word or a compatible word processor.
Hope it can do you a favor.