Documents get returned in books (10)

I believe the answer is:

paperbacks

'books' is the definition.
(paperback is a kind of book)

'documents get returned' is the wordplay.
'documents' becomes 'papers' (I've seen this before).
'get' is an insertion indicator.
'returned' becomes 'back' (I've seen this in other clues).
'papers' placed around 'back' is 'PAPERBACKS'.

'in' is the link.

(Another definition for paperbacks that I've seen is " Popular books".)

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