If you are using PHP 7 under Windows you have to enable ftp in php.ini with extension=php_ftp.dll.
In order to use FTP functions with your PHP configuration, you should add the --enable-ftp option when installing PHP.
The Windows version of PHP 5 has built-in support for this extension. You do not need to load any additional extensions in order to use these functions.
As of PHP 7.0.0 on Windows this extension is always build as shared extension and as such has to be enabled in php.ini.