It's easy to put letters in a file (6)
I believe the answer is:
facile
'it's easy' is the definition.
(synonyms)
'letters in a file' is the wordplay.
'letters' becomes 'ac' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' indicates putting letters inside.
'ac' going into 'file' is 'FACILE'.
'to put' is the link.
Can you help me to learn more?
(Other definitions for facile that I've seen before include "Oversimplified" , "Simplistic" , "Superficial - glib" , "Over-simple, superficial" , "Arrived at without due care or effort" .)