Reviewing treasury papers, including ancient document? (7)
I believe the answer is:
papyrus
'ancient document?' is the definition.
(ancient writing material)
'reviewing treasury papers including' is the wordplay.
'reviewing' is a reversal indicator (I've seen 'reviews' mean this (view the letters another way)).
'including' indicates a hidden word.
'surypap' can be found hidden inside 'treasury papers'.
'surypap' in reverse letter order is 'PAPYRUS'.
(Other definitions for papyrus that I've seen before include "Kind of paper used in old Egyptian manuscripts" , "Egyptian writing matter" , "ancient document" , "Early form of paper" , "manuscript" .)