I have a webform in a .php page and it's function is to send a persons personal information to a payment gateway company via email.

My problem is that to be legally compliant I have to include a field that comes through with the person's information that states the date the form was fillled in (apparently the date the email was received isn't enough).

How do I add a field that doesn't show to the user, but adds the current day's date to the form information?