Magento Open Source 2.1.x

Magento 2.1.x Notice: Magento 2.1.18 is the final 2.1.x release. After June 2019, Magento 2.1.x will no longer receive security patches, quality fixes, or documentation updates. To maintain your site's performance, security, and PCIPayment Card Industry: Refers to debit and credit cards and their associated businesses. compliance, upgrade to the latest version of Magento. The Magento User Guide 2.1.x remains available in PDF for Open Source and Commerce.

Adding Reference IDs to Header

The Order ID and customer IP address can be included in the header of sales documents that accompany an order. By default, both the Order ID and customer IP address appear in the header of invoices, shipment packing slips, and credit memos.