We use the Past Perfect Simple to express an action that was completed BEFORE another past action happened.
"MORE PAST" / "SEPARATE ACTION". We normally do not use the Past Perfect Simple without another past action or another past moment in time for reference. The PAST PERFECT describes an action that was SEPARATE from the other past action/moment in the sentence.
To form the Past Perfect Simple, use..
Subject HAS/HAVE [not] + PAST PARTICIPLE ....
(Aux. Verb) (Main Verb)