If you ever read PDF files on your computer and you don’t have the official (free but huge) Adobe program installed, it’s a fair bet that you’re using Nitro PDF instead. This free program, loved by tens of millions of people around the world, opens PDF files quickly and efficiently but doesn’t suffer from the unnecessary bloat that the Adobe product does.
Source: Free Driver Lets You Print From Any Program to a PDF File | Gizmo’s Freeware