When I open different pdf's I want them to open in separate windows.
It is possible to manually separate the different dokuments after opening them by dragging the tabs.
But it doesn't seem to be possible to set as default that the files open in separate windows.
How do I do that?
Go to preferences (Edit>Preferences - on Windows), or faster is control-K (cmd-K on Mac). Select the General category on the left, and look for the setting labelled 'Open documents as new tabs in the same window', and UNCHECK this. You will need to restart Acrobat for this to take effect.