Conversion RtF to HTML--WINDOW APPLICATION

Imran check these MSDN samples:
https://code.msdn.microsoft.com/Word-Document-Editor-in-d97fd70b
https://code.msdn.microsoft.com/Word-Document-Editor-in-926f019d
They are samples of document editors that use this Word processing component in C#, one for Windows Forms and one for WPF application. In short the samples show how you can manipulate with RTF content in C#, you can use that approach to convert that content to a HTML file or a stream or a string, whatever you need.
For example here is a simple straightforward conversion from one format into another:

DocumentModel.Load("Sample.rtf", LoadOptions.RtfDefault)
                     .Save("Sample.html", SaveOptions.HtmlDefault);

You might be able to do this by loading the RTF file as image, pass it to OCR engine and then save the recognized result as HTML. I know a programming SDK (leadtools) that supports this feature. More details can be found on their website.

I hope this helps.