The principal duties of the secretary of the district shall be to act as secretary of the board and to record and sign all minutes of meetings of the board, including all resolutions and ordinances adopted by the board; to safely and systematically keep all records, files and papers of the board; to safely keep the corporate seal of the district and to affix the same on behalf of the board, and to all certificates by him made as secretary of the district; to sign, execute or acknowledge with the chairman of the board all contracts, deeds, leases or other instruments authorized by the board to be executed by or on behalf of the district, and, if authorized, to deliver the same; and to perform such other duties as may be imposed upon him by law or by vote, resolution or ordinance adopted by the board.