You can download invoices directly from your account. In order to do so, just follow these steps:
Log in to your account
Click on your username in the bottom-left corner of the sidebar and choose Account to access the Account Overview screen
There, click on the Invoices History tab
Once you are there, you will be able to see a list of past invoices. In order to download one, just locate the desired invoice and click on the download icon from the “Actions” column.
Be aware that the invoice you download here is the original one; if you made changes to your billing information after the invoice was issued, those changes will not be reflected here (only invoices issued after the billing information was updated will reflect those changes).