An invoice is basically a commercial document that is issued by the seller to the buyer. It records the entire transaction stating the product description, quantity, agreed price etc. It is indicative that the buyer must pay the seller, according to the terms mentioned on the invoice. On the other hand, a proforma invoice is a kind of invoice. It is used in foreign trade. It indicates a commitment from the seller to provide goods to buyer at specific price. It includes value of customs. It is not a real invoice and is not issues until the seller and buyer have agreed to the terms of the order. Normally it is used for obtaining advance payment from the buyer.
Profoma invoice is issued before goods / services are supplied, while Invoice issued after