Just an idea: source code of Open Office is available. You could download it and see how it works. I think it could be pretty bit work though, even if you try to extract and use existing code.
http://en.wikipedia.org/wiki/Open_Office[
^],
http://incubator.apache.org/openofficeorg/[
^].
Also, Open Office provides the API. There is even the .NET API, but, as far as I know, it's only for OpenOffice native document DOM access. Please see:
http://www.openoffice.org/api/[
^],
http://www.openoffice.org/api/SDK/index.html[
^].
After all, you can always wrap required part of API in .NET by yourself.
—SA