Secured folio placed in prepared prepaid envelope (4,4)
I believe the answer is:
made safe
'secured' is the definition.
Although both the answer and definition are past participle verbs, I can't understand how they can define each other.
'folio placed in prepared prepaid envelope' is the wordplay.
'folio' becomes 'f' (publishing abbreviation).
'placed in' means one lot of letters goes inside another (I've seen this in other clues).
'prepared' becomes 'made' ('make' can be a synonym of 'prepare').
'prepaid envelope' becomes 'sae' (I can't justify this - if you can you should give a lot more credence to this answer).
'made'+'sae'='madesae'
'f' put into 'madesae' is 'MADE SAFE'.
Can you help me to learn more?