Involved in coproporphyrin-dependent heme b biosynthesis (PubMed:25646457). Catalyzes the insertion of ferrous iron into coproporphyrin III to form coproheme III (By similarity). Also catalyzes the decarboxylation of coproheme III to heme b (protoheme IX), the last step of the pathway (By similarity). Fe-coproporphyrin III + 2 H(+) = coproporphyrin III + Fe(2+) Fe-coproporphyrin III + 2 H(+) + 2 H2O2 = 2 CO2 + 4 H2O + heme b Fe-coproporphyrin III + H(+) + H2O2 = CO2 + 2 H2O + harderoheme III H(+) + H2O2 + harderoheme III = CO2 + 2 H2O + heme b Fe-coproporphyrin III acts as both substrate and redox cofactor. Porphyrin-containing compound metabolism; protoheme biosynthesis. In the N-terminal section; belongs to the ferrochelatase family. In the C-terminal section; belongs to the ChdC family.