Fast to knock with papers (5)
I believe the answer is:
rapid
'fast' is the definition.
(similar in meaning)
'knock with papers' is the wordplay.
'knock' becomes 'rap' (synonyms).
'with' means one lot of letters go next to another.
'papers' becomes 'ID' (identification papers).
'rap'+'id'='RAPID'
'to' acts as a link.
(Other definitions for rapid that I've seen before include "Showing pace" , "moving fast" , "Happening at great speed" , "Prompt" , "Fast, speedy" .)