DK has no way to receive goods over its connection, so Stokk makes the file you import instead. It comes from the supplier's invoice on the purchase order, so you never re-key a line.
The invoice number, invoice date and due date are shown on top; click one to copy it into DK.
Stokk warns about lines that need a look but never stops you: an item that is closed in DK, a SKU that seems to belong to another supplier's numbering, a barcode from a different manufacturer, a new SKU that already exists, or lines that don't add up to the invoice. Fix a wrong product with Change match on the invoice, then Rebuild.
Each supplier has Receiving rules on its page under Purchasing → Suppliers: the SKU prefix for new items, and notes on how to read their invoices, such as which items come in cases or how their surcharge is carried. Stokk follows them every time, so add a rule whenever you correct the same thing twice.