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 .OTP extension represent presentation template files created by applications in OASIS OpenDocument standard format. The contents of such a file include presentation information in the form of slides with text, images, shapes, multimedia content, transition effects and other slide elements. These template files are used for creating new presentations quickly based on the styling information stored in the template itself. OTP files can be created and saved with several different applications such as Impress that comes with OpenOffice suite and Microsoft PowerPoint. The OTP file format is similar to Microsoft PowerPoint template files .POT and .POTX.
You can also convert DGN into many other file formats. Please see the complete list below.