With Mountain Lion and Preview you can enter text on PDF forms right on your Mac. Things like IRS forms, school application forms, loan forms, or any of the other myriad of forms that come your way.
Preview (in Mountain Lion) recognizes fields that need to be filled in, boxes that need to be checked and lines that need to be typed on.
When you have the PDF form open in Preview, Preview will automatically change the cursor to an insertion point for a field or a line so that you can begin typing. For a check box the cursor changes to a pointing finger and when you click it adds an X to the box.
To save the modified document just select save from the file menu. And, you can open the document back up and make changes to your entries.
You can also add your personal Signature to a PDF document using Preview. This works in both Lion and Mountain Lion. To see the directions click here.