To Import an Icon from an MDL Resource, DLL, EXE, DGN, or DGNLib File

In the Customize dialog ( File > Settings > Configuration > Customize ) click the Icons tab.
Do one of the following:

Click the arrow on the Import Icons icon and select From MDL Resources.

or
Select From DLL and EXE Files.

or
Select From DGN and DGNLIB Files.

The Select Files to Extract Icons From dialog opens.
Navigate to the file that you want to use and click Open.
The Select Icons to Import dialog opens.
Select one or more icons to import and click OK.