Catalyzes the reversible oxidation of CO(2) and methanofuran (MFR) to N-formylmethanofuran (CHO-MFR). Can only oxidize formylmethanofuran. This enzyme is oxygen-labile. H2O + N-formylmethanofuran + 2 oxidized [2Fe-2S]-[ferredoxin] = CO2 + H(+) + methanofuran + 2 reduced [2Fe-2S]-[ferredoxin] One-carbon metabolism; methanogenesis from CO(2); 5,10-methenyl-5,6,7,8-tetrahydromethanopterin from CO(2): step 1/3. Consists of five subunits; FmdA, FmdB, FmdC, FmdD, and FmdE. By growth on molybdenum, under anaerobic conditions. In the N-terminal section; belongs to the FwdC/FmdC family. In the C-terminal section; belongs to the molybdenum dinucleotide binding protein family.