You should not replace all of a recipe's all purpose flour with whole wheat flour without making any modifications. Whole wheat flour is a bit more dry and needs more liquid than regular white flour. You can substitute half of the regular flour with whole flour in almost any baking recipe and for the most part, the recipe will turn out just fine. But if you want to completely use whole wheat flour, you will have to increase the water and fat in the recipe to keep the dough from turning into a lead weight once baked.