We use the certify method of the SignatureServiceClient as described in
http://help.adobe.com/en_US/livecycle/9.0/programLC/help/index.htm?con tent=000898.html
Because we simply want to sign the form, we create an invisible signature field and pass that to the certify method.
This seems to be a long way around and is in fact causing us problems with the layout.
Question: Is it possible to sign the form not using a signature field?
