Signing Off Digital Style

The Certificate Security option in the Security Method drop-down list in the Document Properties dialog box enables you to digitally sign a PDF document or to verify that a digital signature in a PDF document is valid. Certificate Security is what is known in the trade as a signature handler that uses a private/ public key (also known as PPK) system. In this system, each digital signature is associated with a profile that contains both a private key and a public key.
The private key in your profile is a password-protected number that enables you to digitally sign a PDF document. The public key, which is embedded within your digital signature, enables others who review the document in Acrobat to verify that your signature is valid. Because others must have access to your public key in order to verify your signature, Acrobat puts your public key in what’s called a certificate that is shared. The Certificate Security uses what is known as a direct trust system for sharing certificates, because it doesn’t use a third-party agent (like VeriSign) to do this.