When you save the MS Word document as a webpage, then it in saved with the extension .htm and the format is HTML. When you click on this HTML file, it will open with your default browser.

How to Open CNT Files. A CNT file is associated with Microsoft HTML Help Workshop. Microsoft HMTL Help Workshop is a free program from Microsoft that allows users to develop MSDN articles and ...

Every file on your hard drive (.jpeg, .html, and the like) can be associated with a compatible program, which will open that file format by default.