Documents required for BH series registration in Maharashtra (Pune)

I'm going to get my first Car soon. It's XUV 3XO AX7L AT, and I'm very excited about it. Car has been already been alotted to me and the discussions of payment, insurance etc has started. I want to know what documents are required for a BH series registration in Maharashtra (Pune). I have been doing some research on Google about this and most of the articles says that only a proof of employment is enough i.e ID card or an offer letter from the employer. However the sales person at the dealership wants me to provide them with some Form 20 (or something, don't exactly remember what form) with my employers signature and letter head. This will be very hard to obtain.