This is nothing different from a document file, but you can work on it to publish on web directly as a web form template. This one is the latest feature of word. You have several integrated programs to improvise your templates in terms of visual appearance. You also have the option to work with the add_ons in MS word. If you work wisely, you can bring out a professional template all by yourself.
That's how to create a business letterhead in Word. Now, how do you monetize this new_found knowledge? Offer to your community a letterhead printing service. You can offer to design a logo and print the letterhead. Don't know how to design? Outsource it and then mark it up. Then go to a printing press, get a quotation to print letterheads and then mark it up. But don't mark it up too much. The point is to get as many clients as possible even with a small profits. Several small profits will always add up to big profits.