Publication needing copy to fill page, right? (5)
I believe the answer is:
paper
'publication' is the definition.
(a paper is a type of publication)
'copy to fill page right?' is the wordplay.
'copy' becomes 'ape' (ape can mean to copy or imitate).
'to fill' is an insertion indicator.
'page' becomes 'p'.
'right?' becomes 'R' (common abbreviation).
'p'+'r'='pr'
'ape' going inside 'pr' is 'PAPER'.
'needing' acts as a link.
(Other definitions for paper that I've seen before include "Essay; rag" , "conference presentation" , "It's made from wood pulp generally" , "Dissertation" , "Scholarly article" .)