Hi sandthipe !
First of all warm welcome to world of MODx
Let me add some explanation to my friend’s post...
Create a document group named "Site DOCS". Put all site documents, which you dont want to be viewable to other users, in this document group.
How you will do this, when you edit document, scroll down, you will see
Access permissions Panel, tick the box against "Site DOCS" and hit Save.
Now the other document group members will not able to see the documents,
I think it makes sense, however if you need more help on this, just shout here

and we’ll try our best to help you !
Best wishes and regards,
zi