Having issue using PDFCreator command line

I'm currently using PDFCreator as a converter from docx to pdf. And I'm trying to use python script to invoke the PDFCreator-cli.exe to do the converting job.

The command is simple:
pdfcreator-cli.exe PrintFile /File="xxx.docx" /Profile=Default /OutputFile="xxx.pdf"

It works perfectly when I execute it in the Windows CMD window.
But have error with: 'System.IO.IOException: The handle is invalid' in my python script.
I tried the 'os.system(command)' and the subprocess, but got the same error.

Anyone tried this way to invoke the PDFCreator? Or maybe I need a licensed PDFCreator Server?