How do I edit an invoice or quote that’s been finalized?

A document with a status other than “Draft” cannot be edited.

However, you can change the status back to “Draft” by clicking the current status, then selecting “Draft.” Once this is done, you’ll be able to edit the document again.

Note that companies subject to France’s VAT fraud prevention law cannot edit an invoice once it’s finalized.
In that case, you can cancel the invoice and then create a new one by duplicating the old invoice using the contextual menu located to the right on the invoice list page.