If you are using this homemade pita bread soon after baking and, they have puff up in the oven and still warm. Cut a small section from one end (or cut the bread down the middle) and you will find that the two layers are already separated ready for filling. If the pita bread is cold or has been left stacked for a while the pocket tends to stick. So, the best way to open a pita pocket is to heat them in a pop-up toaster, warm them until they start to puff up. Once they have puffed remove them from the toaster and allow them to sit on a cake rack for a minute or two before cutting and using. I know that this method will open up the pita pockets without tearing for my homemade pita bread and, I am fairly sure it will also work for store-bought pita.