Decomposes formic acid to hydrogen and carbon dioxide under anaerobic conditions in the absence of exogenous electron acceptors. A + formate + H(+) = AH2 + CO2 Binds 1 [4Fe-4S] cluster per subunit. Binds 1 molybdenum-bis(molybdopterin guanine dinucleotide) (Mo-bis-MGD) cofactor per subunit. Inhibited by aerobic conditions. Consists of two separable enzymatic activities: a formate dehydrogenase component (FDH-H) and hydrogenase-3. By formate. Repressed by oxygen, nitrate, nitrite, and other electron acceptors. Belongs to the prokaryotic molybdopterin-containing oxidoreductase family.