blue book vs folder

blue book and folder both are nouns.

Word	Noun	Adjective	Verb	Adverb
blue book	Yes	No	No	No
folder	Yes	No	No	No

As nouns, folder is a hypernym of blue book; that is, folder is a word with a broader meaning than blue book:

Other hypernyms of blue book include booklet, brochure, leaflet, pamphlet.

blue book (noun)	folder (noun)
a register of persons who are socially prominent	covering that is folded over to protect the contents
a report published by the British government; bound in blue	a small book usually having a paper cover
a blue booklet used in universities for writing examinations