Per an Adobe web page, users with the reader should be able to digitally SIGN a PDF but it's not working here. It seems that only users with the Standard edition can SIGN a PDF.
Here's what their webpage says:
"Why should I upgrade to Adobe Reader 8?
A. Adobe Reader 8 enables you to securely view, print, search, sign, and verify the authenticity of Adobe PDF files."
Is there a trick to Reader to sign a PDF?