Unable to retain layers when saving vector PDF in Corel Draw X6 - Help

Having an issue working cross platform with a client who is using Illustrator. He is generating vector PDFs that have layer information. I can open and see the layers if I import the PDF, however if I save or export a PDF with layer information from X6 the layers are flattened. Have checked everything online and the claim is that this should not be happening. How do I save a PDF from Corel Draw X6 and retain the layers?  Thanks.  Version 16.4.1.1281