A change order is a copy of the purchasing document being changed. It enables all of the relevant parties to propose changes on the document by indicating their desired changes to the current version of the document including cancellation of the document.
It is worth noting that the current version is preserved and used as the source of truth for all downstream activities like receipts, invoices, or sourcing against an agreement until the change order processing is complete. It is only after approval, acceptance, and validation of the change order that it gets applied to create a new version of the purchasing document.