BEFORE printing -- required fields MUST be filled out



I'm trying to create a form using required fields. I want the fields to be filled out BEFORE a user is able to successfully print the form.

How can I accomplish this? I know it can easily be done if the form were to be submitted via e-mail, as the PDF checks to see if they've been filled out, but I didn't see any way for the Print button to perform this same check.

Assistance is greatly appreciated.