Ah, I get to answer with the same URL from a previous question. You want to use Win32::OLE to start Word, make a selection, delete the formatting, and prepend/append your HTML markup.

See Word and PERL, the ActivePerl FAQ, and Perl - OLE - Word for some good code to use to start Word. The main thing you'll have to do is figure out the equivalent of the Visual Basic for Applications (VBA) code to do a selection based on formatting

And, as moritz said, you could simply let Word convert the document to HTML and you won't have to do any programming whatsoever