Invoicing

if unregistered dealer is purchasing from registered dealer (assuming GST) and he is selling door to door he can not raise tax invoice or bill of supply since it can be raised by registered dealer regular and composite. by delivery challan it can be given and there is not requirement PAN or Aadhar for billing.

for maintaince of books of account following rules apply whether it is door to door sale or sale in a office or shop.
In relation to any other persons engaged in any other profession or carrying on any business other than section 44AA (1), the requirement of compulsory maintenance of books of accounts applies if- either the income from business or profession exceeds Rs 120000 or the turnover or gross receipts exceed Rs 10 Lakhs in any one of the three years immediately preceding the previous year.

Tnx a lot. 

If a unregistred dealer selling the goods to a registred dealer than what will be the procedure for billing?

just by delivery challan or we can put other name like bill. however it has been kept under RCM previously on that circumstances registered delaer had to generate self invoice.
just simple put any head like bill, challan or any other suitable except tax invoice and bill of supply.