Hello,
We recommend you to read the documentation available on:
https://www.phpdocx.com/documentation/cookbook/working-with-special-characters
https://www.phpdocx.com/documentation/cookbook/convert-html-to-word
about your issue. The most common source of the problem is missing Tidy and mbstring PHP extensions.
If the characters are already as UTF8, you shouldn't encode them again or you'll get a wrong output.
Regards.