Signing a PDF Document
A PDF document can be signed by using the Digital Signature feature in PDF Plus. The author usually signed to indicate his/her approval to the present status of the PDF document. However, a PDF document can contain more than one signature and more than one signer. For example, after a signed PDF is saved as a certified document, another user can be allowed to sign the PDF document when he finishes reviewing.
A signature can be also set invisible, appearing only in the Signatures tab. The Signatures tab shows which changes have been made since each signature was added, and whether the signatures are valid. See Verifying a Signature.