Share Documents feature allows users to give access to documents to other users that may or may not see the room’s folders and their content.
This feature is only allowed in Rooms, it's not available when in Template Mode.
Who can Share Documents?
A user can only share documents to which he has access to and the permissions that he will grant on those documents are equal to or less restrictive than the ones he has on those documents.
The user needs Share Documents room permission and Download Native or Download PDF permission on a folder level. Admin users can always share.