Understanding external references

External references provide additional capabilities not available when you insert a drawing as a block. When you insert a drawing as a block, the entities are stored in the drawing. Any changes you make to the original drawing are not reflected in the drawing in which you inserted it. When you attach an external reference, however, any changes you make to the original drawing file are reflected in the drawings that reference it. These changes appear automatically each time you open the drawing containing the external reference. If you know that the original drawing was modified, you can reload the external reference anytime youre working on the drawing.    

External references are useful for assembling master drawings from component drawings. Use external references to coordinate your work with others in a group. External references help reduce drawing file size and ensure that you are always working with the most recent version of a drawing. However, if you send or receive drawings that contain external references, it is important to include with the master drawing all of the external references attached to it. When you open a drawing that contains external references, the source external reference files must be accessible for the external references to display in the drawing.     

The Xref Manager helps you easily attach and work with external references.