Our company allows customers to pick/use their own domain. I don’t see any mention on the purchase page about multiple-domain support using 1 key, is this something that you offer?
Unfortunately we do not support this use case.
To support an application like this, I would recommend checking out our sister product, PDFTron WebViewer. The API is the exact same as PDF.js Express, so upgrading your POC is seamless. There are no domain limits on PDFTron WebViewer either.
Here’s a link to a form to get you in touch with the PDFTron team.