Cover a page in red fluid (5)
I believe the answer is:
drape
'cover' is the definition.
(I know that cover is the is a more specific form of the action of drape.)
'a page in red fluid' is the wordplay.
'page' becomes 'p'.
'in' is an insertion indicator.
'fluid' indicates an anagram.
'a'+'p'='ap'
'red' is an anagram of 'dre'.
'ap' placed within 'dre' is 'DRAPE'.
(Other definitions for drape that I've seen before include "Hanging cloth used as a blind" , "Spread (cloth over)" , "Pared (anag.)" , "Cover loosely for padre" , "Arrange (cloth) loosely round something" .)