I'm on Windows 7
If I have a directory containing my file é.txt and I start the built-in web server in that directory
php -S localhost:8000
then, using my web browser, I request the URL
http://localhost:8000/é.txt
the web server responds
Not Found
The requested resource /%C3%A9.txt was not found on this server.
PHP's Windows filesystem support is broken - it does not properly translate to the native encoding.
See How do I use filesystem functions in PHP, using UTF-8 strings?