Hello,
That error may appear if:
1. ZipArchive is not installed or enabled. As you can create the DOCX from scratch your server must have ZipArchive installed.
2. The server can't read the DOCX file due to missing read access or it doesn't exist.
3. Some file is missing in the phpdocx folder.
4. The DOCX file you are trying to use as template is not a valid DOCX but a DOC or other document format.
Please run one of the included samples in the examples/Templates/replaceVariableByText folder using PHP CLI mode.
Regards.