You can find directions on our Activation Helppage.
Please note that PDFpenPro is a separate application from PDFpen. If the application you’re trying to register has a green tinted icon and shows PDFpen at the top left of the menu bar, that’s the problem. Please quit PDFpen, drag it to the Trash, and download PDFpenPro. Your activation code should work properly when you launch the newly-downloaded PDFpenPro.
If you need to work without a watermark right away, we recommend that you simply purchase a new, single user license, use that to resolve your immediate need, then contact Nitro to request a refund or to adjust your license to accommodate the number of people who will be using the software.
Please note that single-user licenses allow activation on up to five computers, and you must be the primary user of all activated computers. If you switch computers frequently, please let Nitro know when you do and they will keep your activation count up to date. Multiple user licenses allow for twice the activations as their user count (i.e. 10 activations for a 5-user license). If you have a situation where you need more than that, please let them know and they work with you.