From pip version 23, you can't install a package globally without a managed environment, and the alternative installation method would be using pipx.
But because numpy isn't included in dependencies in pyproject.toml, after the installation you would get the error every time you run pdftext:
ModuleNotFoundError: No module named 'numpy'
The PR #48 fixing this exists and is almost 2 months old.
Please consider reviewing it.