Form 29 and Form 30 explained
Form 29: notice of transfer
The seller signs this to tell the registering authority that the car has been sold. Sellers usually sign two copies: one goes to the RTO and one is kept by the buyer.
Form 30: application for transfer
The buyer signs this to apply for the car to be registered in their name. The seller signs it too, as the transferor.
Deadlines
The law sets short windows. The seller is generally expected to report the sale within 14 days. The buyer generally applies within 30 days, or within 45 days if the car was registered in another state. Check with your RTO, because the details and any late fee depend on your case.
Why it matters
Until the transfer is recorded, the seller's name stays on the RC. That can make the seller liable for challans and accidents after the sale. Keep a signed copy of Form 29 and proof of delivery.