You can not make a word document email body. You have only 2+1 options:
- plain text
- html (restricted css, no javascript):
http://www.thinksend.com/faq/design-restrictions[
^]
- TNEF (this is used when you send RTF with Outlook and Exchange). This would be the nearest to what you desire, but be aware, that this is a really special one. Read this:
http://en.wikipedia.org/wiki/Transport_Neutral_Encapsulation_Format[
^]. I am not sure you will be able to use such format without having exchange server as backend.
As what you want to achieve is platform and vendor-specific, I suggest you forget this approach: create two bodies: plain text and simple html and simply add the word document as attachment.