paperback vs pocketbook

paperback and pocketbook both are nouns.

Word	Noun	Adjective	Verb	Adverb
paperback	Yes	Yes	No	No
pocketbook	Yes	No	No	No

As nouns, pocketbook is a hyponym of paperback; that is, pocketbook is a word with a more specific, narrower meaning than paperback:

Other hyponyms of paperback include pocket book, pocket edition.

paperback (noun)	pocketbook (noun)
a book with paper covers	a container used for carrying money and small personal items or accessories (especially by women)
	pocket-sized paperback book
	a pocket-size case for holding papers and paper money
	your personal financial means

paperback (adjective)	pocketbook (adjective)
(of books) having a flexible binding