We report measurements of the branching fraction and CP violation parameters in B{sup 0}{yields}D{sup +}D{sup -} decays. The results are based on a data sample that contains 535x10{sup 6} BB pairs collected at the {upsilon}(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e{sup +}e{sup -} collider. We obtain 1.97{+-}0.20(stat){+-}0.20(syst)x10{sup -4} for the branching fraction of B{sup 0}{yields}D{sup +}D{sup -}. The measured values of the CP violation parameters are S=-1.13{+-}0.37{+-}0.09, A=0.91{+-}0.23{+-}0.06, where the first error is statistical and the second is systematic. We find evidence of CP violation in B{sup 0}{yields}D{sup +}D{sup -} at the 4.1{sigma} confidence level. While the value of S is consistent with expectations from other measurements, the value of the parameter A favors large direct CP violation at the 3.2{sigma} confidence level, in contradiction to standard model expectations.