To Obtain a User's Certificate via Signed E-Mail

Have the user send their certificate to the author of the file in a signed e-mail.
The user must set the Secure Message Format to S/MIME and check the Send these certificates… box on the Outlook Tool > Opens > Security> Settings > Change Security Settings dialog. Also, turn on the Send clear text signed message on the Outlook Tool > Options > Security tab.
The author then drags the signed e-mail from Outlook on to the desktop or into a folder.
A .msg file is created.
Drag the .msg file onto the Digital Rights dialog in the protected file.
Note: A message signed with clear text has a red certificate seal on the icon. A message signed with non-clear text has a blue lock on the icon.