By navigating to Settings → My Invoices you can find a list of all your invoices. The documents are organized in a list, featuring columns that you can sort by:

Total amount
Invoice number
Due date
Period of the invoice
Date of the last update

There is a search function that you can find in the top right corner of the section. You can search by any data visible on the list.

To download your invoice simply click on the Download button on the right-hand side of the list, in the "Actions" column.