paper-back book vs paperback book

paper-back book and paperback book both are nouns.

Word	Noun	Adjective	Verb	Adverb
paper-back book	Yes	No	No	No
paperback book	Yes	No	No	No

As nouns, paper-back book and paperback book are synonyms defined as:

Other synonyms of paper-back book include paperback, soft-cover, soft-cover book, softback, softback book.

paper-back book (noun)	paperback book (noun)
a book with paper covers	a book with paper covers