Adobe ACROBAT READER 7.0, Manual, Page: 140 / 262

About signing PDF documents
For particular Adobe PDF documents, authors can let users digitally sign documents
whether they use Adobe Acrobat or Adobe Reader. If you open a PDF document that
contains additional usage rights, you can add a digital signature in Reader. (See
About
Adobe PDF documents with additional usage rights .)
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 "behind the scenes" about the person signing a document.
The first signature in a document is called the author signature. The author signature
allows for modification detection and prevention (MDP). In other words, the first time a
PDF document is signed, any change to the document is detected in the Signatures panel,
and the author can determine which changes can be made. For example, an author may
want to ensure that a PDF document with company letterhead isn't changed after it's
signed. Subsequent signatures to the document are called ordinary signatures.
Related Subtopics:
Signing PDF documents in Adobe Reader
Signing PDF documents in a web browser
Changing signature appearance
Setting up Palm OS appearance files
Clearing a digital signature from a signature field