Thanks for sharing your feedback about the recently used documents. We are working on making this feature better in our future releases.
An error occurred while saving the commentAnonymous commented
The solution is that "recommended" documents only shows documents that you (and therefore your colleagues) have access to. Therefore your colleagues will only see "your confidential document" if they have permissions to do so.
If they shouldn't be able to see it then you are storing it/working on it in the wrong place.
The place that is secure to you is your "OneDrive". I recommend that people use their OneDrive and share only with the people that they need/want to see it.