My 5 year old purebred rednose pit won't eat hard food I mix even a tiny handful of hard food with his soft food and he either eats around it or won't touch it... what do I do?

Just give him hard food. He'll eat when he's hungry enough

Have you looked in his mouth to see if there is a cut / teeth issues. If all is good then I would follow Lucky's advice.

How are his teeth?