automatic add of digital certificate?

Hi All, we have a need to automatically add digital signatures to documents, based on the current logged in windows user.  Basically a batch script will complete some information in the PDF document and then we need to have it signed.  We don't want the user to have to open the doc, sign it, save it, and then continue the process.  There must be a way to add the digital signature without having to perform this manual step.  Any help appreciated.

mike