One who pushes paper to insert a cryptic (9)
I believe the answer is:
stationer
'one who pushes paper' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'to insert a cryptic' is the wordplay.
'cryptic' indicates an anagram.
'to'+'insert'+'a'='toinserta'
'toinserta' with letters rearranged gives 'STATIONER'.
Can you help me to learn more?
(Other definitions for stationer that I've seen before include "Poster" , "Shopkeeper" , "Dealer in writing materials" , "source of writing materials" , "Writing-materials shop" .)