Adobe acrobat reader 7.0 Manuale Utente

 

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 

.)

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.