Draw out a former treatise (7)
I believe the answer is:
extract
'draw out' is the definition.
(I know that draw out can be written as extract)
'a former treatise' is the wordplay.
'a former' becomes 'ex' (prefix meaning former or onetime).
'treatise' becomes 'tract' (tract is a kind of treatise).
'ex'+'tract'='EXTRACT'
(Other definitions for extract that I've seen before include "Uproot by force" , "Passage taken from book etc" , "copy out" , "Part" , "Pluck out" .)