official document vs legal instrument

official document and legal instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
official document	Yes	No	No	No
legal instrument	Yes	No	No	No

As nouns, official document and legal instrument are synonyms defined as:

official document and legal instrument: (law) a document that states some contractual relationship or grants some right

Other synonyms of official document include instrument, legal document.

official document (noun)	legal instrument (noun)
(law) a document that states some contractual relationship or grants some right	(law) a document that states some contractual relationship or grants some right