Had initially installed to C:\prg\off\PDF24. I accepted the version upgrade offer from within PDF24 and let it update. The install of PDF24 now ended up in C:\Program Files\PDF24.
This by design or a bug? Could the upgrade process check on install folder and continue to use the same?
I can add to this that it also didn't followed the selection of modules to be installed. First install I excluded the Fax-printer. This was installed with the upgrade.