Thanks for your answer, but your proposal will not work. Like I wrote in the initial post, we intend to install PDF24 exactly the same way than Windows installs Security Updates with the option "Shutdown and install updates" from the Windows start menu. In this phase, the user session is already closed and there is no user interface available at all. When performing an installation that will prompt for anything during this phase, the installation will hang "by design".
Performing the installation interactive without any switch in the user session will not work (the user has no admin rights), and when the user has admin rights, the problem does not appear.
Regards, Franz