An external reference (xref) inserts the entire contents of another drawing into the current drawing as a display-only object.
External referencing is a standard AutoCAD function, using commands XATTACH and EXTERNALREFERENCES. On the ribbon, click View tab 
Palettes panel External References Manager.
You cannot edit objects in the referenced drawing, but you can use Layer Manager to control the display of separate components.
For more information, see the AutoCAD help topic "Attach Drawing References (Xrefs)."