Kristy,
Users will need PGP installed to read PGP encrypted material. That is, unless they are receiving a message via Web Messenger or PDF Messenger. Depending on how the mail policy is set up by a PGP Universal Server administrator they may have it set up to use this service when sending a secure message to external users.
If there is a secure message policy that enables PDF Messenger try sending the message with a subject header [PGP]. You can also try select the pgp encrypt button when sending the message.
You can find addional information on how PDF Messenger works from the PGP Universal Server admin guide: http://www.symantec.com/docs/DOC3598. If PDF Messenger is set up correctly the encrypted PDF Messenger message should be encrypted to the recipients Web Messenger passphrase.
Regards,
Mike A.
PGP Technical Support
Symantec Corporation