Company adopting revolutionary doctrine (5)
I believe the answer is:
credo
'doctrine' is the definition.
(I know that credo is a type of doctrine)
'company adopting revolutionary' is the wordplay.
'company' becomes 'co' (abbreviation).
'adopting' indicates putting letters inside (inserted letters are taken on or adopted).
'revolutionary' becomes 'red' (informal term for communist).
'co' placed around 'red' is 'CREDO'.
(Other definitions for credo that I've seen before include "set of ideas" , "piece of sacred music" , "Set of beliefs about leftist circle" , "Section of mass" , "Formal statement of beliefs" .)