editing a pdf file with Acrobat Standard 8.0

I recently received a form from acustomer that they would like for me to change. When I used the tools menu and went to touch up document I received the follwoing message. "All or part of the selection has no available system fonts. You cannot add or delete text using the currently selected font."

Can someone please advise me onw hat I need to do to edit this document and change the words.
Thank you,

Rick Meyer