There are 3 ways to download your invoices in PDF format.
1. Go to Billing page and scroll down to invoices table. Click on Show all invoices. There you can see and download all invoices based on date.
2. Go to Billing page and scroll down to orders table. Find your order and click on "View" or it's ID. There you can click on Download Invoices to download all invoices related to that order.
3. Go to the invoice page and click on PDF icon.