This page will help you select the appropriate license for your usage of PDF/Mergician. If you still have any question, then do not hesitate to contact sales.

PDF/Mergician Professional

End User You need this license to edit, create or interactively merge Merge Projects (*.pmf files). One license is required for each user using PDF/Mergician Professional.
Server You need this license to run PDF/Mergician Professional as a web service, form receiver or run PDF/Mergician Professional unattended from the command line. One license is required for every PC on which the PDF/Mergician Professional Web Service, Form Receiver or Console Application is installed.

Note that at least one End User license is needed to create/edit Merge Projects. No additional licenses are required for users accessing the server remotely.
End User + Server This bundle is not a seperate license type. It is a commercial package that contains the combination of an End User and a Server license.

General

Single v.s.
5 Seat
All licenses are activated on a single PC. The seat number gives the number of PC's you can activate the license on. So a Single Seat license can be activated on one PC and a 5 Seat license can be activated on five PC's.
Upgrade subscription The optional Upgrade Subscription adds 1 year of free major upgrades. Subscribers will receive all product releases (bug fixes, minor updates and major upgrades) during the 12 month subscription.
Additionally the upgrade subscription gives you the right to reset your license once a year for changes computers, employee changes etc.

More information here.