There is no way to trace back a response to the form filler. You need to include an email address field on your form to capture this information.
Thanks, we figured that, so we included the email address in the new version.
If we really really have to know who send the reply, does Adobe keep their IP address or some sort of data to protect yourself for which it is available but not openly available ?
We currently do not provide IP addresses of form fillers to form authors. The best way for you to verify who fills out your form, is to control who you distribute the form url to.