Fun is editing leader for paper (8)
I believe the answer is:
treatise
'for paper' is the definition.
(I've seen this before)
'fun is editing leader' is the wordplay.
'fun' becomes 'treat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'leader' indicates taking the first letters.
The initial letter of 'editing' is 'e'.
'treat'+'is'+'e'='TREATISE'
Can you help me to learn more?
(Other definitions for treatise that I've seen before include "Written exposition of an argument" , "Formal piece of writing on a particular subject" , "Thesis" , "A written work about treaties" , "Formal written work dealing with a particular subject" .)