Please upgrade the PDF Document Generation module to the latest one. Then use 'Mendix Coud Dedicated' option and it will work.
Hi Jasper,
I'm afraid it's because you're running on the Siemens cloud. The documentation states that "currently we support Mendix Public Cloud and Mendix for Private Cloud". Maybe you can try in a Mendix Sandbox or locally whether you've setup everything else correct.
Good luck!