Can anyone tell me what happens when a user's certificate expires after
they've signed a form?  The scenario:

UserA signs a form.
2 weeks later his certificate expires and a new certificate is issued

What happens when UserB opens the form? Do they get a message...can they see
that the form was signed by UserA?  

Thanks in advance for help on this.

If anyone has any resources on this subject I'd be very grateful.  

f any people from the InfoPath team are reading this, it would be very
helpful to post a blog article on setting up active directory to manage
certificates for InfoPath forms.  There's a lot of information on the web
about using digital signatures but very little on how to set up a network to
manage digital certificates for InfoPath.