If you suspect or know that he had papers at one time then you can call and ask the registry if they will match DNA. Because of rule changes over the years many registries have either parent verification done which means foal, mare and sire all have DNA on file so there is a record of DNA for the horse in question or just DNA typing which means there is DNA on file that could be matched to. If he is on file with the registry then that is simple. Either he will match something in the database or not. Some registries may or may not offer that as an option.