Do you want to prevent other people to open your drawing?
I think that if you have an important drawing, you should lock it. In this part, I will give tutorial to you do this.
Step 1: You open AutoCAD drawing that you need to lock.
Step 3: AutoCAD will open security options dialog box, you can input password here and must choose this encrypt drawing properties option, after clock click Ok. AutoCAD will ask you confirm password > click Ok.
Step 3: Now you can save drawing.
Step 4: Checking, when you open, AutoCAD will ask you to enter password to open drawing
This protection can help you to prevent other users open drawing, but remember, you must remember that password, if not you never open it again.