fill in vs inform

fill in and inform both are verbs.

Word	Noun	Adjective	Verb	Adverb
fill in	No	No	Yes	No
inform	No	No	Yes	No

As verbs, inform is a hypernym of fill in; that is, inform is a word with a broader meaning than fill in:

fill in (verb)	inform (verb)
supply with information on a specific topic	give character or essence to
write all the required information onto a form	impart knowledge of some fact, state of affairs, or event to
represent the effect of shade or shadow on	act as an informer
be a substitute