Drawing files that have DGN underlay attachments can be plotted or published as DGN files and DGN underlays are tracked and managed when you eTransmit. Furthermore, DGN underlays are not lost when you save to previous drawing formats.
When a drawing file containing an attached DGN underlay is plotted or published, any visible DGN geometry is included with the plotted or published drawing file.
A DGN underlay that is attached to a drawing is saved along with all other content that makes up the drawing. Upon reopening the drawing, the DGN underlay is present unless the path to the DGN file has changed in some way. In this case, a bounding box containing the path to the missing DGN file is displayed along with the model that was selected when the DGN file was attached. Once the path is restored or a new path is specified, the DGN underlay will appear in the drawing.
If you save the drawing to a previous DWG format, the DGN underlay is not going to be displayed when the drawing is opened in an older version of AutoCAD. The DGN underlay will display again if you reopen the drawing in the current version.
DGN attachments are tracked and managed when you eTransmit in the same way raster image attachments are tracked and managed.