1. Import your Gerbers and Drills in to FAB 3000. (menu: File / Import / AutoLoad...)
2. Assign Layer types.
3. Go to menu: Tools / DFM / DFM Check...
4. Review options, and press Next.
That's it, FAB 3000 will quickly find all DFM Violations in your gerbers. Here's a tutorial showing these steps, plus generating a PDF file that you may share with colleagues.