To find your invoice you will first need to log in to your account and click "MY OFFICE".
Afterwards you will be directed to your "My Office" page where you will next click "Order Management" and in the dropdown click "Order Details". You will be able to find your order number and you can click anywhere in that row to go to the next page.
You can click the black "Invoice" box and your invoice will popup onto the same screen.
You can see the invoice or print it out if you wish.