Strong paper for book (4,5)
I believe the answer is:
hard times
'book' is the definition.
(I've seen this before)
'strong paper' is the wordplay.
'strong' becomes 'hard' ('hard' can be a synonym of 'strong').
'paper' becomes 'times' (The Times newspaper).
'hard'+'times'='HARD TIMES'
'for' is the link.
(Other definitions for hard times that I've seen before include "old book" , "work with social relevance" , "Stealers of things" , "Possibly description of our crossword" , "Book by Dickens" .)