The Document that is displayed when you first install says:
Is it FREE?
The FREE EDITION comes with a limit of 3 Notebooks, and a total of 20 Pages per Notebook. Depending on how prolific a writer you are, this may be sufficient for some time. For others, purchasing a license removes these restrictions, allowing you to create any number of Notebooks and Pages.
This is normal - and the same document (explaining the FREE EDITION) also appears when first starting the "LICENSED VERSION".
After activating - the software should be shown as the "Licensed Version"
Check this in the Help -> About Dialog. View Here
The LICENSED Version will not have the "3 Notebook restriction", and will permit additional notebooks to be opened.
The Instructions for using PageFour can be displayed by pressing F1 while running the program (or loaded separately from the start menu).