For the purpose of any investigation or examination under RSA 383-A, RSA 383-B, RSA 383-C, and RSA 383-D, the commissioner shall have the power to subpoena witnesses and administer oaths in any adjudicative proceedings and the power to compel, by subpoena duces tecum, the production of all books, records, files, and other documents and materials relevant to his or her investigation or examination.