Do I really need pastry flour in my molasses cookie recipe?
Pastry flour is a lower protein flour than the regular flour. From here 


  the protein content of any given type
  of flour determines how tender,
  strong, elastic, stretchy, pliable,
  etc., the dough is that you make with
  it, and also the texture of the
  finished bread, waffle, cookie,
  croissant, etc.


So basically using regular flour rather than using the pastry flour might mean that your cookies will be denser. 

If you don't have pastry flour you can always google substitutes. That what I do if I don't have something. I saved money by not buying another flour by just adding cornstarch to the regular flour I already had.