We do not support delayed fulfillment of orders for pending payments with Authorize.Net; we can only fulfill orders immediately following checkout if they are paid via Authorize.Net. If an authorized payment is placed "on hold" at checkout and then settled manually at some later point separately, after the buyer has completed their checkout, Authorize.Net has no way to inform our system of that completed payment.
We do have a setting (in Seller Admin > Payment Preferences) to "Only Authorize" all payments at the time of checkout without settling the actual charge, so you could review and settle such payments manually later, but in that case our system would still process the sale as soon as Authorize.Net authorizes the amount for payment without waiting for subsequent settlement of the actual payment.
To fulfill downloads manually for such pending payments, you can issue download links using your Seller Admin > "Send free download link" feature. However, if you're using our PDF Stamping feature, that method would not engage the Stamper, because there's no checkout being performed to send buyer data to the Stamper; however, there's another way you can manually issue a free link for a Stamped PDF -- see this page for further instructions.
