Thank you for your feedback, @slowkow. I’m pleased to say that in the new Paperpile web app, in beta, we listened to feedback from beta testers, and now you copy the PMID directly from the reference details in your library. You can do this by clicking on the dots menu beneath a reference, right-clicking on the PMID and copying it. And I’ve recorded your request for having the DOI accessible within the PDF viewer for consideration by the team in the future.