Release a document as a matter of choice (4,4)
I believe the answer is:
free will
'choice' is the definition.
(ability to make choices)
'release a document as a matter' is the wordplay.
I cannot really understand how this works, but
'release' could be 'free' (synonyms) and 'free' is present in the answer.
'document' could be 'will' (will is a kind of document) and 'will' is found in the answer.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for free will that I've seen before include "The ability to choose" , "The power of choosing own course of action" , "Ability to change future" , "ability to act without direction" , "Volition" .)