Document X is recorded (7)
I believe the answer is:
written
'is recorded' is the definition.
(I've seen this in another clue)
'document x' is the wordplay.
'document' becomes 'writ' (writ is a kind of document).
'x' becomes 'ten' (X is the Roman numeral for ten).
'writ'+'ten'='WRITTEN'
(Other definitions for written that I've seen before include "Expressed on paper" , "Penned" , "Transcribed" , "Put down on paper" , "taken down" .)