Hi
Payment Form doesn't store credit card number in it's own database. If you use a credit card payment method like Paypal Pro, Authorize.net..., you will need to purchase an SSL certificate for your site to make payment transactions secure .
If you don't use credit card payment method (or example, just use Paypal Standard), you don't have to worry about security here in Payment Form because all the payment process are happens at the Payment gateway site (Paypal site for example) .
Hope my answer is clear to you .
Regards,
Tuan