When I change the view, for example: from “list view” to “columns view”, the selected document has to be selected once again in order to see its preview. Can this (annoying 
) extra step be avoided by means of other settings?
Thanks in advance!
Changing from the List view to the Columns view (and back) should retain the selected document, at least that is the behavior I see here. However, changing from some views e.g. Split to Three Panes will lose focus if the selection was a document. Groups, however will still retain the focus.
If you are only switching views to preview a document, using the spacebar when a document is selected may be a better option.
You’re right: I mean switching between “list view” and “three panes view”.
I wanted to switch quickly to the “three panes view” to include some highlights without having to open the document. (spacebar won’t do that for me).
I don’t know why the document gets unselected in the “three panes view”, while in all the other view modes the problem doesn’t exist.
Because all the other views show groups and documents in the list section of the view (not to be confused with the List view). The Three pane view only displays groups in the list section of the view. It is literally splitting groups and documents into individual sections, thus the name ‘Three Panes’.
For me that’s not a reason to unselect my selected document when I switch to that view. I don’t see why what you are saying would be incompatible with keeping the document selected. Just show the groups in the list section of the view and then at the right (above) the list of documents with the selected document selected and at the right (under) the preview of that document.