Have you double-checked the PDF options... you might have collected some security in the conversion...
... although if it works on Mac and not on Windows it is probably a bug.
If you generate a PDF in windows not in FIleMaker... does it do the same thing?
thank you for your suggestions. I contacted FileMaker Support in Switzerland and got the answer, that they are aware of the problem, but can not give me a date, when the fixwill be available. In the meantime we switched back to 12.0.3 and everything is fine.