Hi there.
Convert .pdf file from color to grayscale with 1 command:
gs
-sOutputFile=./output.pdf
-sDEVICE=pdfwrite
-sColorConversionStrategy=Gray
-dProcessColorModel=/DeviceGray
-dCompatibilityLevel=1.4
-dNOPAUSE
-dBATCH
./input.pdf
And You’re all done. Change the input.pdf and output.pdf to your needs.
Cheers.
Andrzej
PS.
[root@wishmasus andrzejl]# which gs
/sbin/gs
[root@wishmasus andrzejl]# pacman -Q --owns /sbin/gs
/sbin/gs is owned by ghostscript 9.14-1
[root@wishmasus andrzejl]#