This document provides instructions for adding an existing product to a Paytm Mall catalogue and submitting required brand authorization documents. To add an existing product, search for it on Paytm Mall and click "Add to Your Catalogue". Some products require authorization documents like a brand letter or trademark certificate, which can be submitted through the Seller Helpdesk after selecting the Listing & Catalogue tab and filling out the submission form. The product will go live within 2-3 business days after validating details and submitting.