The following command will convert the PDF.

Useful for cases when colors are wrong after the import by PDF Light Viewer plugin:

gs -dSAFER -dBATCH -dNOPAUSE -dNOCACHE -sDEVICE=pdfwrite -sColorConversionStrategy=CMYK -dProcessColorModel=/DeviceCMYK -sOutputFile=some.rgb.pdf some.pdf