To Open a DGN File from the File Tab

Select File > Open, and click Browse.
The File Open dialog opens.

The default file filter is "CAD Files [*.dgn, *.dwg, *.dxf]."
(Optional) Select the desired WorkSpace and WorkSet from the respective drop-down lists.
(Optional) To change the filter, select the desired filter from the drop-down list next to the File name field.
For example, changing the filter to "All Files [*.*]" displays all files in the current directory.
(Optional) Navigate to the desired drive or directory.
Do one of the following:

In the list box, select the desired DGN file.

or
In the File name field, key in the name of the desired DGN file.
Click Open.
Note: To open the file with "read-only" access, in which design modifications cannot be saved to disk, click the down-arrow next to the Open button and select Open Read-Only.
(Optional) If the file is not part of the selected WorkSet, you get an alert window, mentioning that the file is not part of the WorkSet or is part of another WorkSet. Make the desired selection in the alert window and click Open.

Note: By default, a thumbnail of the DGN file is created when the DGN file is saved. This thumbnail displays in the preview window on the File Open and Open dialogs. You can disable the creation of thumbnails by changing the MS_THUMBNAIL configuration variable to NONE (all uppercase).

Note: If a DGN file has never been opened, the Bentley insignia displays in the preview window. If the DGN file has been saved but no thumbnail was created, the preview window is empty.