documental vs documentary

documental is not a noun while documentary is a noun.

Word	Noun	Adjective	Verb	Adverb
documental	No	Yes	No	No
documentary	Yes	Yes	No	No

As adjectives, documental and documentary are synonyms defined as:

documental and documentary: relating to or consisting of or derived from documents

documental (noun)	documentary (noun)
	a film or TV program presenting the facts about a person or event

documental (adjective)	documentary (adjective)
relating to or consisting of or derived from documents	relating to or consisting of or derived from documents
	(of film, television, radio, or photography) depicting a real-life event using images or interviews with people involved in the event