You are able to subscribe on PayPal automatic (recurring) payments - you can use funds on your PayPal account to pay for our services, or you can link your credit or debit card to your PayPal account, and use funds from this card for making automatic payments. You can read more about using your credit or debit cards with PayPal here.
Also you can add extra funds (bonus) on your account, which can be used for paying all new documents automatically, with function "Autopay".