Therefore, Doug is mortal. A valid argument is one where the conclusion follows from the premises. Thus it is impossible for a valid argument to have true premises and a false conclusion. All that matters is that the conclusion follows from the premises. Validity is a relation between the premises and conclusion.
All geniuses are philosophers.
Portmore is a genius. Therefore, Portmore is a philosopher. Either Portmore is wearing a watch or socks. He isn't wearing a watch. Therefore, he is wearing socks.