folder vs blue book

folder and blue book both are nouns.

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

As nouns, blue book is a hyponym of folder; that is, blue book is a word with a more specific, narrower meaning than folder:

Other hyponyms of folder include ticket book.

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