How to add Digital Signature on Sales Invoice Print

Hello Everyone,

I am looking for Digital signature,Its a certificate in a pen drive with validity.

Currently user save sales invoice document from AX in PDF and attaching digital signature from pendrive in PDF and reprinting the document in which digital signature with user name is appearing on the document.

I want to call this certificate in AX it self during print of document.

Is it possible in AX 2009?