Hello,
We recommend you to check your server logs, the reason of generic errors such as 'Internal server error' must be added to a log. Maybe you are getting some timeout or you don't have read access to the files. The problem 'The site can't be reached error' doesn't come from phpdocx, please check your server log to know the source of it.
We also recommend you to test the included samples using the PHP CLI mode and with local files, to know if the problem is related to remote access or the server itself.
Regards.