are bread flour and all purpose flours interchangeable?

If a recipe calls for 1 cup all purpose flour and I use 1 cup whole wheat bread flour will I completely ruin it?

You generally add about 1/3 to 1/4 of the amount of flour required as AP flour. But bread and AP are interchangable. Bread flour is just higher gluten, so it comes out with a finer texture. You'll be fine!

If it were me, I'd do 1/4c AP flour and the rest whole wheat. I've never had much luck doing it all whole wheat. You might also need a little more moisture too.

HTH!