Convert Pdf from color to GrayScale using Ghost Script 8.57

gswin32.exe -sOutputFile=%2 -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH %1

First Parameter is Input PDF Path, Second Parameter is Output PDF Path

This command also convert a pdf into version 1.4.