the passive in German

Fine as far as it goes, but the whole point/problem of the so-called Passive is that 'to be + PP' in English can be one of two things. 'The door was closed' either means that is how it was, closed; or it means something happened: by forces or persons unknown the door was closed, clunk. The first is no problem: was closed = war geschlossen; if you can see that the other is different, then all you have to do is to remember to use different verb werden to express that.