Hello,
Your username doesn't have any license tied. Please send to contact[at]phpdocx.com the username or email of the user that purchased the license you are using.
Regarding your question, we recommend you read the documentation available on https://www.phpdocx.com/documentation/practical/creating-a-new-document.
phpdocx includes an autoloader. When you require/include CreateDocx.php, all classes are available to be used. The phpdocx namespaces includes its own autoloader and can also be used with Composer to autoload classes.
Please note that this a PHP question. On https://www.php.net/manual/en/language.oop5.autoload.php you can read more information about how PHP autoloaders work.
Regards.