Top journalist hiding page that's filled out (7)
I believe the answer is:
plumped
'filled out' is the definition.
('plump' can be a synonym of 'fill out')
'top journalist hiding page' is the wordplay.
'top' becomes 'plum' (plum can mean excellent or top-class).
'journalist' becomes 'ed' (short for editor).
'hiding' is an insertion indicator.
'page' becomes 'p'.
'plum'+'ed'='plumed'
'plumed' going around 'p' is 'PLUMPED'.
'that's' acts as a link.
(Other definitions for plumped that I've seen before include "fattened up" , "Chose" .)