how can I add Paypal to jotform?

After creating a Paypal account you can select Paypal from the Payment tools menu on the left:

To use Paypal pro you need to have a merchant account. You can see here more details on Paypal forms:

https://www.jotform.com/help/165-Setting-Up-Your-First-Order-Form 

https://www.jotform.com/help/50-PayPal-Forms 

https://www.jotform.com/help/183-Difference-Between-PayPal-PayPal-Pro 

Let us know if we can assist you further.

https://www.jotform.com/help/285-Configuring-PayPal-Express-Integration