Converting PDF from RGB to CMYK with freeware or OSS

Original post: https://graphicdesign.stackexchange.com/a/38313

gswin32.exe
    -o -o c:/path/to/output-cmyk.pdf
    -sDEVICE=pdfwrite
    -dUseCIEColor
    -sProcessColorModel=DeviceCMYK
    -sColorConversionStrategy=CMYK
    -sColorConversionStrategyForImages=CMYK
    input-rgb.pdf