Do customers get their invoices by email?

Each new invoice is emailed to the customer in your company's name, with your logo, the lines, total, due date and your bank details, or marked Paid, thank you if already paid. It has a button to view and download the invoice.

This is on by default. To stop it, untick the invoice emails switch in Setup → Invoices. Imported invoices are never emailed. You can always copy an invoice's link from the Invoices tab with Copy link.