DGN files are drawings created by and supported by CAD applications such as MicroStation and Intergraph Interactive Graphics Design System. It is used for creating and saving designs for construction projects such as highways, bridges, and buildings. The format is similar to Autodesk’s DWG file format and is considered its competitor.
Files with .htm extension represent Hypertext Markup Language for creating web pages for display in web browsers such as Google Chrome, Internet Explorer, Firefox, and a number of others.
You can also convert DGN into many other file formats. Please see the complete list below.