Files with DWG extension represent proprietary binary files used for containing 2D and 3D design data. Like DXF, which are ASCII files, DWG represents the binary file format for CAD (Computer Aided Design) drawings. It contains a vector image and metadata for the representation of the contents of CAD files.
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 DWG into many other file formats. Please see the complete list below.