A person who bears witness or gives testimony

Someone who attests or officially certifies something

प्रमाणित करने वाला

English Usage: The attestor signed the document to certify its authenticity.

Hindi Usage: प्रमाणित करने वाले ने दस्तावेज़ पर हस्ताक्षर किए ताकि उसकी सत्यता की पुष्टि हो सके।