Ray's pup ruined document (7)
I believe the answer is:
papyrus
'document' is the definition.
(papyrus is a kind of document)
'ray's pup ruined' is the wordplay.
'ruined' indicates an anagram.
'rays'+'pup'='rayspup'
'rayspup' is an anagram of 'PAPYRUS'.
(Other definitions for papyrus that I've seen before include "Ancient paper plant" , "Egyptian material for writing on" , "ancient document" , "Paper made from reed by ancient Egyptians" , "Paper made from reeds" .)