If you export goods using UPS, and have paperless customs forms and invoicing enabled on your UPS account (if not you can enroll here).
To enable Shiptheory to use paperless invoices for UPS, in Shiptheory under your UPS advanced settings in Shiptheory you can enable paperless billing.

You will need to be using either Brightpearl or Magento and have your commodity information set accordingly:

Brightpearl Commodity Codes

Magento Commodity Codes