How to create a PDF in gray-scale - not in colors?

How to create a PDF in gray-scale - not in colors?

I want to create a PDF with a script from a programm (e.g Access) and I've tried to get a JPG in gray-scale with "JPEGColorscount = 1" and i worked out great.

But I'm not able to get a PDF in gray-scale - tried "PDFColorsColorModel" - but id didn't work out - the PDF is still colored...

Can anybody help me with the right settings for making a gray-scaled PDF with command-script

Many thanks for help from Austria