User manual

About digital signatures
A digital signature, like a conventional handwritten signature, identifies the person signing a
document. Unlike traditional signatures on paper, however, each digital signature stores information
about the person signing a document. Signatures help prevent unwanted changes to a PDF document.
For example, an author may not want a PDF document with company letterhead to be changed after
it's signed. (See Signing Adobe PDF documents.)
The first signature in a document is called the author signature. When you add the first signature to a
document, you have the option of certifying the document. Certifying a document lets you attest to its
contents and specify the types of changes allowed for the document to remain certified. Changes to
the document are detected in the Signatures tab. Subsequent signatures to the document are called
ordinary signatures.
To sign a document, you must select a digital ID, which contains the signature information that you
can share with other users in a certificate. You can create a self-signed digital ID, or you can obtain a
digital ID from a third-party provider. Using certificates, other users can validate your signatures, and
you should validate the signatures of others. (See Using digital IDs and certification methods.)
Note: For the latest information about digital signatures, choose Help > Online Support to open the
Adobe Acrobat support page on the Adobe website, and then search for "digital signatures."
Valid digital signature in a PDF form