Hi and welcome to SaleHoo Ama,
Suppliers of authentic brands should provide you with official authentication paperwork when you purchase these products.
Please note that we cannot guarantee that our Chinese suppliers will always offer authentic brands where advertised. We suggest that you contact the supplier directly and inquire about the product you wish to purchase. Request that they provide you with a proof of authenticity for their products, as most brand name items come with official paperwork for the resale of these items.
I'm not sure if there is a specific document other than those already mentioned. But you should at all cost avoid buying brand name items from China.
All the best :)