Does cooking add calories to food?
It depends whether or not you're adding something caloric to your food! If you fry it, yes. Oil/shortening contains calories. Eating food+oil contains more calories than the food alone. If you boil it in water, no. water has no calories. Heating the food in an oven or microwave will not add any calories.
It is important to remember that food preparation certainly can change the nutritional values of a foodstuff. When you start adding caloric items such as butter or sugar to a product, (surprise, surprise) you'll end up with more calories to the finished item. Sometimes, especially in the case of salads, added dressing or cheese can end up having many times more calories than the vegetables themselves. Be aware of this when making food choices.