Generally speaking, pizza boxes are not designed to be heated in the microwave. This is because pizza boxes are usually made of cardboard or paper materials, which may not be able to withstand high temperatures and microwave radiation. If you put a pizza box in the microwave, it could set the box on fire or release toxic chemicals.
Therefore, if you plan to reheat your pizza in the microwave, it's best to transfer the pizza to a microwave-safe container, such as a glass bowl or ceramic dish. Not only does this avoid safety issues, but it also ensures that the pizza is heated more evenly, making it tastier. Also, make sure the microwave is heated for the right amount of time and power to avoid overheating or burning food.