credential vs written document

credential and written document both are nouns.

Word	Noun	Adjective	Verb	Adverb
credential	Yes	No	No	No
written document	Yes	No	No	No

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

credential: a document attesting to the truth of certain stated facts
written document: writing that provides information (especially information of an official nature)

Other hypernyms of credential include document, papers.

credential (noun)	written document (noun)
a document attesting to the truth of certain stated facts	writing that provides information (especially information of an official nature)