Adobe Acrobat 7 Professional - Manual (Page 45)

Document security
Acrobat 7.0 offers enhanced security features, including more robust signature validation.
You can create Adobe PDF documents by using security policies that can expire and
revoke documents, as well as maintain accountability by keeping track of who opens
protected documents.
You can bundle attached files into a secure electronic envelope (eEnvelope) designed to
protect documents during transit.