You are better off trying to physically repair the DVD surface so it will read cleanly. There are several companies that sell scratch removers and surface polishers.
If your DVD is damaged to the point you can see through the scratches in the recording layer when you hold it up to the light, then no amount of polishing will help.
You can use software like
ddrecue to pull off as much data as possible, but remember:
- it will take a looong time,
- the filesystem will be damaged