Document copy pair keeps (5)
I believe the answer is:
paper
'document' is the definition.
(e.g. scientific paper, white paper)
'copy pair keeps' is the wordplay.
'copy' becomes 'ape' (ape can mean to copy or imitate).
'pair' becomes 'pr' (abbreviation).
'keeps' means one lot of letters goes inside another (inserted letters are kept inside).
'ape' going inside 'pr' is 'PAPER'.
(Other definitions for paper that I've seen before include "Maybe Times" , "Journal" , "Threat that seems powerful (but is just a pussy cat!)" , "Sort of clip" , "Short essay" .)