And doc and docx are MS word extentions. rtf is rich text format and is open, so you can create them in a lot of text editors. txt is pure text and you can do it in the text editor that comes with mac (can't remember the name as I usually use word wrangler). odt is open office.
Yes, I discovered that I would need MS Word and there was all sorts of complicated carry on re an important document which was required but the recipient is willing to take the document via email. I am completely crap at this sort of thing.