Concerning a manuscript, you need lots of paper (5)
I believe the answer is:
reams
'lots of paper' is the definition.
(I've seen this before)
'concerning a manuscript' is the wordplay.
'concerning' becomes 're'.
'manuscript' becomes 'ms' ('ms' can be a synonym of 'manuscript').
're'+'a'+'ms'='REAMS'
'you need' is the link.
(Other definitions for reams that I've seen before include "Large quantity of written matter" , "Large quantities (of paper?)" , "Scrapes the barrel" , "Lots of paper" , "This much paperwork" .)