Takes in cover and old sheet (8)
I believe the answer is:
foolscap
'old sheet' is the definition.
'foolscap' can be an answer for 'sheet' (foolscap is a kind of sheet). I am not sure about the 'old' bit.
'takes in cover' is the wordplay.
'takes in' becomes 'fools' ('fool' can be a synonym of 'take in').
'cover' becomes 'cap' (capping is a kind of covering).
'fools'+'cap'='FOOLSCAP'
'and' is the link.
Can you help me to learn more?
(Other definitions for foolscap that I've seen before include "something near A4" , "sheet" , "Cop's foal (anag)" , "About 330 x 200 (or 400) mm size of paper" , "Paper or book size (from its watermark)" .)