This Tense is used to express an action which was over long ago. In this tense the third form of the verb is used.
The formula for past perfect is Subject +Aux + V3
I had eaten an apple six years ago.
We had eaten apples six years ago.
We had eaten apples six years ago.
You had eaten an apple six years ago.
He had eaten an apple six years ago.
She had eaten an apple six years ago.
It had eaten an apple six years ago.
They had eaten apples six years ago.