Stick poster on this page? (6)
I believe the answer is:
adhere
'stick' is the definition.
(to adhere to something is to stick to it)
'poster on this page?' is the wordplay.
'poster' becomes 'ad' (short for advert).
'on this page?' becomes 'here' (I've seen this in another clue).
'ad'+'here'='ADHERE'
(Other definitions for adhere that I've seen before include "secure" , "Stay attached" , "Header (anag)" , "Cling, attach" , "Hold fast, stand by" .)