Hi Niraj,
InfoPath does this when it opens the form before OnLoad code is called. I don't think there's a way to intercept it. You can't strip it out before InfoPath opens because InfoPath checksums the signature to the XML and it would no longer match which would cause failure to open. You might be able to launch InfoPath with the /aggregate switch and send the form to it and then have some OnMergeRequest logic strip it out, but then what's the value of signing it in the first place?
Patrick Halstead [InfoPath MVP]
InfoPathDev
Patrick Halstead
Project Manager at Qdabra