Can you convert a Savage 30D 12g shotgun to pistol grips?

If you mean "can I find the parts to install a pistol grip and vertical forearm onto a Savage model 30D 12 ga pump shotgun?" then the answer is almost certainly no. While the butt stock and forearm come off the 30D easily enough, the gun hasn't been manufactured since 1978. No company is manufacturing aftermarket parts for a 30 year old gun. Any such parts would have to be hand made.

Note: federal law requires a shotgun to have a minimum barrel length of 18", measured from the face of the closed breech to the muzzle, and a minimum overall length of 28"