Does anyone know of any Plug-ins that will allow multiple users to add comments to the same PDF concurrently?

This is the only PDF plug-in that I could find available on Forum that has wide functionality forum.appian.com/.../summary There are features to add content to a PDF via process but I don't think it would really support concurrency. You may want to give it a try, if it doesn't help with your requirement you might need to build your own or not support concurrency by locking the file during the edits forum.appian.com/.../Lock_Document_Smart_Service.html