Required to facilitate the formation of correct disulfide bonds in some periplasmic proteins and for the assembly of the periplasmic c-type cytochromes. Acts by transferring electrons from cytoplasmic thioredoxin to the periplasm. This transfer involves a cascade of disulfide bond formation and reduction steps. [protein]-dithiol + NAD(+) = [protein]-disulfide + H(+) + NADH [protein]-dithiol + NADP(+) = [protein]-disulfide + H(+) + NADPH Belongs to the thioredoxin family. DsbD subfamily.