how to sign a pdf document with sea horse?

["J.A.Aylward" <J A Aylward exeter ac uk>]

Sorry if this is a dumb question, but I've been trawling the web and the 
seahorse archives for an answer and can't find one.

In an openoffice document you can sign a document with a digital 
signature, and it's all contained within the document.

Right clicking on a document in Gnome, produces a menu-item "Sign" - 
which duly produces a .sig file. with seahorse

..so what do I do with it? ;-)

Have I just got the wrong impression, and the signing of a file is for 
signing other certificates to make them "trusted"
or should I be somehow embedding the signature file within the pdf?

Thanks in advance

Jamie Aylward