Document decision
Packing slip vs invoice
A packing slip identifies what is in a shipment; an invoice identifies what is owed.
First option
Packing Slip
Use this when it reflects the business event at its current stage. Add only facts you can support, then keep the resulting local record with its context.
Next distinct event
Invoice
Use this when the workflow has moved to a genuinely different event. A different layout alone never turns one document into another.
Practical rule
Choose by purpose, not by template.
The workspace permits only supported conversions and keeps provenance where a new document is a real follow-up record. Review the number, parties, dates, and totals before export.