A 997 is also known as a Functional Acknowledgment. This file is sent to confirm receipt of a document (a 997 will never be sent back for an other 997). That confirmation is important to trading partners because it lets them know that their document has been received. Because of this, your trading partner may require you to send back a 997 for each document they send you. Please check with GCommerce if you are unsure as to whether or not your trading partner requires a 997 to be returned.