If you're looking for a PDF invoice of your order you can find it in two places.
First place you can find it is on your shipping confirmation email.
You should see a link at the bottom of your shipping confirmation email that will allow you to view your invoice.
Second is from your Account page on the portal
You will find a list of orders on this page, and there is an option to click on the "Print Invoice" button located on the right-hand side of the page.