Encryption protects the contents of the PDF document and lets you restrict certain
Adobe Actobat display functions. The Adobe Acrobat password features let users access
protected documents and restricted functions.
Adobe Acrobat supports the use of certificate signatures (also known as digital signatures), which let you sign PDF files with a certificate-based digital ID. This certificate
ID is issued by a trusted third-part certificate authority, such as CAcert.org or
VeriSign.