You can send copies of your FormKeep receipts directly to an email address.
The setting is a little hidden though, so here's a walkthrough of changing it.
Goto Settings->Payment and press the View Billing History button.
At the bottom of the displayed window is a link to Receipt Settings where there is a checkbox and a place to enter the email that should receive the emailed receipts.
You can also enter any extra billing formation to be included on the receipts automatically.