Hi Matthias,
Syncfusion PDF Viewer does not have support to set the print orientation while printing the PDF document. We will print the PDF document with the default A4 size. If the provided PDF document width is greater than the height, then we will rotate the page and we will print the same. This is the default behavior of Syncfusion PDF Viewer for printing the PDF documents.
Please revert to us, if you need further assistance.
Regards,
Dhivya.