Validate Field Text Before Submit

Hello, I´m bulding a website ecommerce and I need to register some specify user based an unique code. I need to validate a field text before submit, which checks for user nif (or another field, like ID) in a database. I need a form field with validation (the user has to enter a valid user nif. If the value is not matching with the database value, he\she can’t register. Is this possible to do using Use Registration?

The page I need help with: [log in to see the link]