This is a very tough one. Before I go in to detail about who would win, we have to acount that doctor doom is one of the most bad ass vilains of marvel. He has apeared in almost every marvel comics series. He has faced off some of the badest characters in the marvel universe.
On the other hand Iron man is onr of the greatest heores in the marvel universe. He has some of the greatest weaponry and technolgy. He has a vast number of suits and upgrades them. He is a founding member of the avengers and has fought some of the badest vilains in the marvel universe.
I think doctor doom would have the uper hand at first and beat iron man down pretty hard. After that , doom would start to become over confidant in himself. He would monolog. Iron man could use this time to use it to his advantage. I say iron man beacuse vialins have a superority complex and over lock things which is why they lose most of the times, but I am not saying that doctor doom would lose easily he give iron man a run for his money.