You can get an invoice for the order by clicking on the "Generate invoice" button from the "Documents" section. The invoice is also generated once you put the order in the "Payment accepted" status.
Once it is generated, the "View invoice" button below gets activated the top-bar.
You can customize the invoice layout easily: the PDF template files are located in the
When you put the order in the "Preparation in progress" state, a delivery slip PDF is generated, which you can then download from the "Documents" section.