Just downloaded DFMNow to give it a try.
I loaded up my gerbers and they view fine.
I tried many combinations of options to print to PDF (using PDFCreator as the printer) and it always fails...
Thanks for submitting a support ticket.
I would suggest that you print to PDF using a different PDF printer like "Microsoft Print to PDF" (as we cannot provide technical support for PDFCreator).
Here's a quick tutorial (no sound) showing me use DFM Now to Print to PDF using Microsft.https://numericalsoftware-update.s3.amazonaws.com/tutorials/2018-08-02_7-31-44dfmnow_pdf.mp4
Note: There are hundreds of other PDF printers to try if you don't wish to use Microsoft.