You can do what you want in either VB or VC++.
Before you get into either language, please see and familiarize yourself
with the Word Object Model. There is a valuable Microsoft Knowledge Base
article that will help. It is Q222101 - How to Find and Use Office Object
Model Documentation

You can retrieve it from the web using the address:
http://www.*-*-*.com/

If you are proficient in both VB and VC++, consider using VB, and look at
the Web site
http://www.*-*-*.com/
On that page note the link to
Q184974 - How to Use (OLE) Automation With Word

If you are proficient in only VC++ look at the web page
http://www.*-*-*.com/
On that page start with the first article on the page - Q178149 - HOWTO:
Create Automation Project Using MFC and a Type Library,
then look at any of the articles in the section titled "Automating Word"

None of the articles written for the VB programmer or the VC++ programmer
show you exactly what you want to do. All of them are meant to help solve
more complex application needs. But you can see many of the concepts for
which you're looking.

All you need to do is create the instance of Word, use that instance to
open the particular document, then save it using SaveAs... with a filetype
of HTML, then release all the object references and close Word.

VC++ doesn't understand VB named variables, so you need to follow the
advice in the article Q222101 - How to Find and Use Office Object Model
Documentation  to see how to get the numeric equivalents to the VB named
variables.

Microsoft does not support nor recommend automating any of the Office
applications in an unattended mode. The applications are all desktop
applications, so you need to have a real person monitoring your application
when it automates Word.  Please see the Knowledge Base article Q257757 -  
INFO: Automation of Office for Unattended Execution is Not Recommended or
Supported. There is a link to that article on either of the pages
http://www.*-*-*.com/
or
http://www.*-*-*.com/

Hope this helps.