Adobe Reader 8

About digital signatures

A digital signature, like a conventional handwritten signature, identifies the person signing a document. Unlike a handwritten signature, a digital signature is difficult to forge because it contains encrypted information that is unique to the signer and easily verified.

Most digital signatures are referred to as approval signatures. Signatures that certify a PDF are called certifying signatures. Only the first person to sign a PDF (most often, the author) can add a certifying signature. A certifying signature attests to the contents of the document and allows the signer to specify the types of changes allowed for the document to remain certified. Changes to the document are detected in the Signatures panel.

To sign a document, you must obtain a digital ID or create a self-signed digital ID in Reader. The digital ID contains a private key that is used to add the digital signature, and it contains a certificate that you share with those who need to validate your signature.
Note: You cannot create self-signed digital IDs from within FIPS mode.

When you apply a digital signature, Reader uses a hashing algorithm to generate a message digest, which it encrypts using your private key. Reader embeds the encrypted message digest in the PDF, along with details from your certificate, a visual representation of your signature, and a version of the document at the time it was signed.

Note: For the latest information about digital signatures, choose Help > Online Support > Knowledge Base to open the Adobe Acrobat support page on the Adobe website, and then search for “digital signatures.”