Wants paper in reserve shortly (8)
I believe the answer is:
requires
'wants' is the definition.
('require' can be a synonym of 'want')
'paper in reserve shortly' is the wordplay.
'paper' becomes 'quire' (paper measurement).
'in' means one lot of letters goes inside another.
'reserve shortly' becomes 'res' (I've seen this in other clues; 'shortly' asks for a short form).
'quire' inserted within 'res' is 'REQUIRES'.
(Other definitions for requires that I've seen before include "Has need of" , "Needs or demands" , "Demands or wants" .)