The document discusses the past perfect passive voice in English. It explains that the past perfect passive is used to describe something that had been done by someone before another time in the past. It provides the structure for forming the past perfect passive and examples of its use. The key differences between the past perfect active and passive voices are that the passive allows the object of an active sentence to become the subject and de-emphasizes the subject. The past perfect passive expresses previous actions or states that began in the past and continued up until another point in the past.