Important one goes through papers? (6)
I believe the answer is:
staple
I believe this clue is a double definition.
'important' is the first definition.
'one goes through papers?' is the second definition.
(Other definitions for staple that I've seen before include "essential" , "Fastening wire" , "Paper-fastening device" , "(Of food) necessary and important" , "A wire paper fastener for plates" .)