When you selected "All releases" for your question, you made it almost impossible to answer. There are different releases of TeamRoom, with different features.
In the current release there is a button at the top of the document: Mark Private. I think this restricts access to the author and the reviewers. The reviewers can be defined as one or more of the TeamRoom's subteams.
If all the users are readers, and only one person can create documents, then you are not using your TeamRoom the way it was intended to be used, because the team members cannot participate. To me, this indicates that your team has a problem.
Also, a group of people will not function as a team if information that is available to some is hidden from others. To me, it seems that restricting access to documents will only make your team's prblem worse.