Kruser6 said:
Pepperoni--particularly frozen pizza pepperoni--is damn near indestructable. While that might not bode well for your digestive system, its not going to go bad. If there's ever a nuclear holocaust all that will remain will be cockroaches and cured meats like pepperoni...
This might also be a case where the cheaper the pizza the longer its unfrozen shelf life--or in this case "counter life". The more expensive frozen pizzas use better cheese with fewer preservatives.
In any case, you're probably safe with a basic frozen (or "unfrozen") pepperoni pizza....good luck to you!