Search notes:

Registry: HKEY_CURRENT_USER\Software\Classes\ms-officeapp\Shell\Open\Command

If the default value of HKEY_CURRENT_USER\Software\Classes\ms-officeapp\Shell\Open\Command is set to rundll32, the so-called hyper key is inactive.

The following cmd.exe command does exactly that:

C:\> reg add HKCU\Software\Classes\ms-officeapp\Shell\Open\Command /t REG_SZ /d rundll32

This modification can be undone by deleting the entire registry key:

C:\> reg delete HKCU\Software\Classes\ms-officeapp\Shell\Open\Command