Hi Deb,
Have you purchased and installed the Digital Signature on the computer?
You may refer to the following link ‘Add or remove a digital signature in Office files’ and check if it helps.
Also for issues with Digital Signature in Office application, I would also recommend you to post your query in the Office IT Pro forum for better suggestions.
http://social.technet.microsoft.com/Forums/en-US/officeitprolegacy/threads
I hope the above information helps. If you need further assistance, you may reply and I’ll be happy to assist you.
Thank you.