A lot of document converters are built on c#. If you are developing the one and want to spend minimum time to produce high-quality functional Doc to xHTML converter, you may take ready word to xHTML library like Total Doc ConverterX and use it as a basis for your application. It is a server version of desktop Total Doc Converter that can serve either as standalone app or become a part of some existing server application. That is why it is perfect for creating a new service or enhancing the existing one.
In order to integrate this Word xHTML c# converter into your project, you may do the following:
Total Doc ConverterX is very powerful converter that can turn Doc files into web pages, graphic files, texts or text tables. You can not stop only on integrating Word to xHTML conversion mode, but also take advantage of other available modes. All they are available in one library. Setting conversion options is made by specifying proper convert Word to xHTML command line parameters. Users (or automatic program) can send conversion commands to a server application and get files converted according to the settings.
It is possible also to perform conversions via user interface, to make it more comfortable for inexperience users. You need to built-in Total Doc ConverterX using ActiveX technology, able to port features of one tool into another. ActiveX is provided together with converter SDK.
One more advantage is ability to adjust automatic conversion. It is useful, if you need to provide regular Doc to xHTML conversions of some specific file storage. For this you need Total Folder Monitor. The upcoming Doc sources can be automatically converted by this Word to xHTML server converter. You can try all that by your hands, just download an SDK here.