Generating a monochrome PDF file from a color PDF file
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 & White.
- Save and you're done.
You can also use Ghostscript to transform color into grayscale PDFs. The most recent version is v. 9.05, which is the recommended one for this task.
Commandline:
gs \
-o grayscale.pdf \
-sDEVICE=pdfwrite \
-dPDFSETTINGS=/prepress \
-sColorConversionStrategy=Gray \
-sColorConversionStrategyForImages=Gray \
-sProcessColorModel=DeviceGray \
-dCompatibilityLevel=1.4 \
/path/to/input.pdf