written report vs papers

written report and papers both are nouns.

Word	Noun	Adjective	Verb	Adverb
written report	Yes	No	No	No
papers	Yes	No	No	No

As nouns, papers is a hypernym of written report; that is, papers is a word with a broader meaning than written report:

written report: a written document describing the findings of some individual or group
papers: writing that provides information (especially information of an official nature)

Other hypernyms of written report include document, written document.

written report (noun)	papers (noun)
a written document describing the findings of some individual or group	writing that provides information (especially information of an official nature)