If you are taking payments through the Stripe payment gateway, you can toggle on "Include Stripe receipt email in the checkout" under Configure → Payments to have Stripe automatically send a receipt for the purchase.
Paperform supports sending a standard payment and submission summary as text in the body of an Email Response, as a PDF submission summary attached to an Email Response, or a Custom PDF. Here's more on these:
1. Choose "Receipt" as the content of the email
2. Or, if you choose the "Custom Message" option, you can optionally append the receipt to the end of your custom email.
3. Attach a Custom PDF, that you'll need to have already created via "After Submission → Custom PDFs".