"The door was opened."
Translation:De deur werd geopend.
No, I'm sorry but that is not correct. 'To be' and 'zijn' are used differently and that can be a bit confusing.
In English you use a form of 'to be' + past participle to form the passive. So the simple past is 'was opened' and the past perfect is 'had been opened.'
In Dutch you use 'worden' + past participle for the simple present and simple past, but you use 'zijn' + past participle for the perfect forms. So the simple past is 'werd geopend' and the past perfect is 'was geopend