Instead of saving it as a new file format, you have to DOWNLOAD it as a .docx file. File>Download as>Microsoft Word (.docx). Save it to your Chromebook (or whatever computer you are using), then you can just attach it to your email as a docx file. There is a caveat. While this works, sometimes formatting gets messed up. This doesn’t seem to be nearly as much of an issue as it used to be, but it can still happen.