When you do document conversion on LiveDocX, you need to do a mailmerge and then retrieve the document. Even though you aren't inserting any new content, you need to do a mailmerge that replaces a dummy placeholder with dummy content.
So, the process I'd suggest is:
1) Set your source document as local template
2) Merge a dummy field with dummy content
3) Retrieve your document as HTML
4) Use a script server side to remove the html and leave only the content (Something like, remove everything between the HEAD tags, then strip_tags on the rest)
5) You should be left with your content as a simple string - I'm not sure it'll be too meaningful, but might be useful for building something like search indices.