GO:0004748:   ribonucleoside-diphosphate reductase activity, thioredoxin disulfide as acceptor
Catalysis of the reaction: 2"-deoxyribonucleoside diphosphate + thioredoxin disulfide + H2O = ribonucleoside diphosphate + thioredoxin. Thioredoxin disulfide is the oxidized form of thioredoxin.