Question

the manager opened the door (change the voice).​

Answer 1

THE DOOR WAS OPENED BY THE MANAGER

HOPE IT MAY HELP.......!!!

Answer 2

The manager opened the door.

This sentence has been written in active voice. If you ask me to change its voice, I would write it in passive voice like this:

The door was opened by the manager.

In passive voice, the subject takes place of the verb and becomes more important in the sentence. The word 'by' is an important component of passive voice sentences, which is often used to interchange the places of verbs and subjects in the sentence.