Fast and easy to use cross-platform .NET library that creates or modifies Microsoft Word (DocX) and later also Excel (XLSX) files without installing any software. Library is based on Open XML SDK
Save as HTML basically means translating every single paragraph to HTML. Thats a project on its own. While I am toying with this idea there are other projects that try adres this
I looked through all the samples but did not see any mention of saving a docx as a "Web Page" like Word provides in the Save menu.
I did see mention of cloning issues, but that sounded like it was related to saving a new docx.