While light-weight pdf readers are a very good alternative to "Adobe Reader" and there are more reasons other than just the bloat to use them, but there are times when a user needs to rely upon the official PDF reader from Adobe. Today we will see how to use free utility software "Adobe Reader X" to digitally sign a document, a digital signature or e-signature is a mathematical encryption technique used to ensure authenticity of a digital message or document. A valid digital signature gives a recipient reason to believe that the message was created by a known sender, and that it was not altered or tampered with in-transit.