Generating a monochrome PDF file from a color PDF file How can I generate a monochrome pdf file from a color pdf file?

I have tried ImageMagick's convert, but with bad results.

A direct conversion


  convert -monochrome file.pdf file-bw.pdf


produces dithered images.

Going through png


  convert -monochrome -background white -geometry 2048 file.pdf file-bw.png


stubbornly keeps the background to some shade of gray.
You can do this easily in Preview:


Open the PDF in Preview.
Go to File > Export...
From the Quartz Filter drop-down box, select Black &amp; White.
Save and you're done.