Substituting pancake mix for flour
Are you sure that's all that is in your pancake mix? You normally have some baking soda, baking powder, oils, salt, sugar, corn starch in there (You'll find all of these in Bisquick, plus some conditioners to make the gluten stronger and things like that). Possibly some egg and milk products depending on the type of mix. 

Even if that's all the stuff in your baking mix, you don't necessarily know how much baking powder is in there to compensate for in your recipe (you may need to add more or the pancake mix may have too much leavener). Too much baking powder can affect texture (not structurally sound enough) and flavor (bitterness). 

That being said, you may want to experiment. Some recipes will take better to substitution of the pancake mix than others. See also this question. 

However, if you have only one shot at the recipe (or don't want to deal with the possible wastage of ingredients), go buy the appropriate flour. And then use the pancake mix for pancakes (or not great waffles; despite the marketing spiel on the box, pancake mix makes for OK pancakes and bad waffles).