唔明依句句子點解??(好奇怪)

The boy is hiding in one of the cupboards.

Take away "in his possession" and the meaning of the sentence does not change much.

The boy had papers containing questions set by his teacher.

"Had" is the verb and papers the object.

"In his possession" is an adverbial phrase which can be placed at the end of the sentence. "In his possession" means the boy physically possessed the question papers. But the best position is placed the phrase right after the verb "had", as the original sentence does.

The main idea of the sentence:-
The boy(s)had(v) papers(o).
in his possession=adv phr
(to be) placed at end of ,or after "had" as shown in the sentence.
had been=eg:-I had been suffering a bad time in the cupboard.
had been=eg:-The boy had been suffering a bad time by hiding in the cupboards. You are incorrect by placing been before had=been had?
eg:-according to your idea:-The boy been had suffering a bad time by hiding in one of the cupboards!
had=past tense of "have"=get the papers.