As for PDF Reader Pro.dmg：
If you want to unbind your license code to one device and link it to another, please contact firstname.lastname@example.org to claim your request with your license code and email address. We will unbind it for you.
As for PDF Reader Pro (Apple Store):
Download PDF Reader Pro from Apple Store with the same Apple ID in your new device and open it. You don't need to pay for a second time.