There is no such "conversion" simply because there is no one-to-one correspondence between Word and HTML. You can do something, but the input should come in two parts: the document itself and some mapping model to map the two, a set of mapping rules or something like that.
Word itself provides some "Save as HTML" operation, but it was always criticized as highly bloated. I must admit that visually, in last versions of Word, the result imitates original document very closely and looks pretty neat, but past conversions were a disaster.
To work with Word, you can use MS Office Interop Word. Please see:
http://msdn.microsoft.com/en-us/library/microsoft.office.interop.word%28v=office.14%29.aspx[
^],
http://msdn.microsoft.com/en-us/library/ff597928.aspx[
^],
http://msdn.microsoft.com/en-us/library/ff601860.aspx[
^].
Good luck,
—SA