We're sorry you've encountered trouble activating PDFpenPro.
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 write us to request a refund or to adjust your license to accommodate the number of people who will be using the software.
If your need is not immediate, please send us the exact text of the error you're encountering, and we'll respond to you promptly.
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 us know when you do and we'll 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 us know and we'll work with you.