Customers sometimes request to have an invoice sent to them for an order placed online. If they have registered for an online account they can log in to the website and download the invoice from the My Account area.
Alternatively you can print the invoice to PDF by doing as follows:
Select the order in Big Commerce Orders section
Select "Print Invoices for Selected"
Click "Confirm"
When new window comes up change "Print Destination" to "Save as PDF"
Save PDF on desktop of computer you are using, and then email to customer as attachment
NOTE: using the "Resend Invoices for Selected" option only sends a copy of the confirmation email again, not an actual PDF invoice