How do I set a file to have UTF-8 encoding, when I am converting the file into a Leanpub book?

Sometimes when authors try to upload files and convert them into Leanpub books, they encounter an error related to UTF-8 encoding.

Here are some instructions for encoding a Word file as UTF-8:

https://support.office.com/en-us/article/Choose-text-encoding-when-you-open-and-save-files-60d59c21-88b5-4006-831c-d536d42fd861

You may also find this article helpful, if you are trying to set a file to UTF-8 encoding in Windows in Notepad:

http://help.leanpub.com/author-help/how-do-i-set-my-book-to-save-with-utf-8-character-encoding-on-windows-in-notepad