Only the account owner can access your invoices within Fathom.
To do this:
Login to Fathom
Select the Administration menu (cog icon) from the top right menu
Select "Account / Billing", and then view the "Invoices" tab
Download any past invoice as a .pdf
Email my invoices
From this screen, you're able to specify an email address to send your invoices each month.
Simply scroll down to the bottom of the screen and add an email address in the "Email my invoices" field. The above video shows more detail.