Not Responding when Saving a PDF

I am trying to combine a large number of pdf files into one large pdf binder. I am able to combine, and search them the file once it is combined, but when i try to save it, i get a "Not Responding" message. Sometimes Adobe stops working and closes and sometimes it just freezes up and i have to end task using task manager. Anyone have any idea of what would cause this and how i can fix it?

Thanks