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.