Hello,
The relative path is correct if you run the sample in the same folder than the script. Please check that all files have been copied and you are running the script in the same folder that the script exists; as it uses a relative path, you can't run:
C:\...>php.exe examples/Core/addText/sample_1.php
You need to access the examples folder and then run the script:
C:\...> cd examples/Core/addText
C:\...> php sample_1.php
You can also try to set an absolute path to CreateDocx.inc, and also please check you can include CreateDocx.inc correctly.
The error you are getting only appears if PHP can't read the file.
Regards.