Hard to produce fake documents? (5)
I believe the answer is:
rigid
'hard' is the definition.
(I've seen this before)
'fake documents?' is the wordplay.
'fake' becomes 'rig'.
'documents?' becomes 'ID' (identification).
'rig'+'id'='RIGID'
'to produce' is the link.
(Other definitions for rigid that I've seen before include "starched too much?" , "Stiff and inflexible" , "Unable to bend" , "completely" , "unwilling to move" .)