As a PRO user, you now have access to receipts for your monthly or yearly bill. They will live forever in your account under the PRO settings page so you can always access them. You'll see this widget with a list of each billing. Click the Plus to reveal what the billing was for.
Click the link to see the actual receipt.
If you print this page, it has a nice print stylesheet so it comes out real nice-like:
You can also click the Email button, type in an email address, and send it to whoever might need it.
Now get to printing those receipts! Definitely a business expense, right? You can write it off for sure. Or slip it into your expense report at work. It'll be fine.
As an aside, isn't it weird how many apps call them "invoices"? I guess it kinda makes sense as a "paid" invoice", but we think "receipt" makes more sense.