File opened directly from Windows file explorer => cmdline = gerbv.exe "FILEPATH"
Didn't check on non-Windows OS. Version is newest release.

No special characters:

File contains ö:

Opened from inside the application; to exist/open or not to exist/open, that is the question:

Directory (and File) contains ö:
-> same as File contains ö

Open file button clicked:

Opened from inside the application (it CAN display the contents, just open the dir from within the open dialog ...)
-> Schrödingers file again.