Currently the Greyscale/mono options are not enabled, due to inconsistent support across physical and virtual printers.
You can either pre-process the PDF, see link below, or edit the settings of the target printer your self.
Currently the Greyscale/mono options are not enabled, due to inconsistent support across physical and virtual printers.
You can either pre-process the PDF, see link below, or edit the settings of the target printer your self.