folio vs page number

folio and page number both are nouns.

Word	Noun	Adjective	Verb	Adverb
folio	Yes	No	No	No
page number	Yes	No	No	No

As nouns, folio and page number are synonyms defined as:

Other synonyms of folio include pagination, paging.

folio (noun)	page number (noun)
a book (or manuscript) consisting of large sheets of paper folded in the middle to make two leaves or four pages	the system of numbering pages
a sheet of any written or printed material (especially in a manuscript or book)
the system of numbering pages