Users of any permission level can leave messages and upload documents to their own or other profiles. Who can see these posts will be determined by the settings you apply when you share a post.
Just me - This means that when sharing the post, your colleagues and managers will not be able to view it. However, admins will still be able to view these posts.
Everyone - This means that all other users will be able to view the post.
Only Admins - This means that only admin users will be able to view the post.