The work area (user interface) > Viewports > Drawlist > Lock a viewport's drawing list
  
Lock a viewport's drawing list
1. Open the Structure Browser.
2. Right-click in the Structure Browser and click Drawlist > Locked on the context menu.
Creo Elements/Direct Modeling locks the viewport's drawlist. While locked, you cannot add, remove, clear or copy objects in the drawlist.
To unlock a viewport's drawlist
1. Open the Structure Browser.
2. Right-click in the Structure Browser and click Drawlist > Locked on the context menu.
Creo Elements/Direct Modeling unlocks the viewport's drawlist. Any objects you now create are added to the drawlist.
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Any objects that you create while the drawlist is locked are automatically added to the drawlist but given the status hidden. You must unlock the drawlist and then click on the object's icon.