The problem is the standard temp directory where the docx files will be created by phpdocx. When I use it, it will give me empty docx files. I don't know exactly why.
In my own project folder I made a folder 'generetedDocs' with write permissions for apache.
I made the createDocx and createDocxAndDownload methods working with the new path:
$docx->createDocx($_SERVER["DOCUMENT_ROOT"] . '/generetedDocs/example_text');
$docx->createDocxAndDownload($_SERVER["DOCUMENT_ROOT"] . '/generetedDocs/example_text');
now I've good filled docx files!