Currently, the API does not support downloading merged PDFs with markups when the active user is not the session host. While the API can download copies of the PDFs uploaded to a session, those files do not include markups added during the session.
We have already built an internal tool that allows staff to batch download files from Studio Sessions available through their Bluebeam accounts. The only missing capability is the ability to download those files with the associated markups included, which is where most of the value resides for us.