When to use the passive
Verbs can be used in active or passive form. This depends on whether you would like to emphasize the performer of an action or that someone or something is affected by an action.

(Passive) He was forced to resign.
(Here the emphasis is on the he being affected by the resignation.)

(Active) The senior management forced him to resign.
(Here the senior management is emphasized as the performer or the initiating party of the resignation.)

The passive is also used when the performer is unknown or, too obvious to mention or when the action is more important than the performer. Such cases are often seen in law, medicine or scientific reports.

However, for general use, especially when communicating with members of the public, you should avoid overusing the passive. Use the active voice whenever possible, this helps you to create a more direct, personal and forceful tone in writing.