When the PDF Invoice add-on is enabled, both a store administrator and a customer get a PDF invoice attached to the order confirmation email if the "Send the invoice attachment in the mail" option is enabled:
A store administrator can open a PDF invoice for one or several orders at a time using the bulk order editing feature on the order listing page (Orders -> Orders List) in the store's Admin area:
For this purpose, it is necessary to:
Select the order(s) from the order list in the Admin area (Orders -> Orders List).
Click the "Open PDF invoices" button at the bottom of the listing page.
Invoices for the selected orders will be downloaded in PDF format to the admin's computer, where it will be possible to open and use them further.