The licensing of PDF Architect is based on a yearly license fee per user (subscription). The license includes the usage as well as the latest updates and ongoing support. It is managed through user accounts. License keys are not required. For each "named user" a license is needed. If you own several licenses you can assign these to other users.
PDF Architect FAQ
Along with the installation of PDF Architect you will be regularly informed about upgrading opportunities that might suit your needs. For example, if you’re only using PDF Architect’s free modules it will inform you about discounted upgrades to PDF Architect Standard or Pro package by sending a desktop notification every now and then.