I want to convert a color pdf to black and white pdf in specific mode I want to convert all text in red or green in black (not in gray).
gs -o output.pdf \
-sDEVICE=pdfwrite \
-dBlackText=true \
-dBlackVector=true \
-sColorConversionStrategy=Gray \
-dProcessColorModel=/DeviceGray \
input.pdf
