No MS Word, Yes PDF.

There is a very lengthy and very good article on why MS Word documents are bad for email. I personally find them more problematic than many other formats.

Here is a quote that should scare some of you into avoiding using MS Word in emails:

Microsoft Word is often configured by default to automatically track and record changes you make to a document. What many people do not realize is that this record of changes is actually silently embedded in the file every time you save your document. When you send such a document to a third party, it is a trivial matter for them to recover this log and see how the document appeared several revisions ago. Thus compromising or confidential information you thought you removed from a document before sending it may in fact still be accessible to the recipient.