As you found out, your QlikView NPrinting Service account must be exclusive to NPrinting and not shared with any other service. Please see the Windows User (Dedicated to running the NPrinting Server Service) section in this document: Requirements for NPrinting 16.x.x.x versions only
I am not sure about QlikView but NPrinting only needs the QlikView NPrinting PDF Printer which is installed as part of the setup process.
A NPrinting service account was created and NPrinting was installed under that user.
This is happening every two weeks with pdfsaver3.exe and pdfsaver5.exe will show up as services under NPrinting and cause issues. Once we end the pdfsaver services and restart NPrintinf runs and completed the scheduled tasks.
I know at one time there were QlikView reports that ran as pdf but now they are all being do under NPrinting.
Are you aware of any issues resulting if PDF-Xchange was uninstalled?