EDI X12 is the dominant electronic-data-interchange standard in North American B2B commerce, purchase orders (850), invoices (810), ship notices (856), payment remittances (820). Used by Walmart, Amazon, Target, every large retailer's supply chain. Plain text with delimiter conventions declared in the ISA header.
How to open
Specialized EDI software (Stedi, Cleo, OpenText). For analysis or debugging: convert segments to CSV for spreadsheet review.