mandatory vs obligatory

mandatory is a noun but obligatory is not a noun.

Word	Noun	Adjective	Verb	Adverb
mandatory	Yes	Yes	No	No
obligatory	No	Yes	No	No

mandatory (noun)	obligatory (noun)
a territory surrendered by Turkey or Germany after World War I and put under the tutelage of some other European power until they are able to stand by themselves
the recipient of a mandate

mandatory (adjective)	obligatory (adjective)
required by rule	morally or legally constraining or binding
	required by obligation or compulsion or convention