Catalyzes the reversible oxidation of CO(2) and methanofuran (MFR) to N-formylmethanofuran (CHO-MFR). This enzyme is oxygen-labile. May function as an electron transfer protein. H2O + N-formylmethanofuran + 2 oxidized [2Fe-2S]-[ferredoxin] = CO2 + H(+) + methanofuran + 2 reduced [2Fe-2S]-[ferredoxin] Binds 2 [4Fe-4S] clusters. Not inactivated by cyanide. One-carbon metabolism; methanogenesis from CO(2); 5,10-methenyl-5,6,7,8-tetrahydromethanopterin from CO(2): step 1/3. By growth on tungsten or molybdenum under anaerobic conditions.