I opened a PDF form with GraphicConverter and found that by using the text tool, I could fill in the blank form spaces as needed. On a multi-page PDF file, only the page actually open would be saved.
After filling in and saving all the pages, I used a freeware program called CombinePDFs to restore to the original multi-page PDF.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20041008200236437