Change the color model of an included pdf

Say I have a pdf file `foo.pdf` that I want to include in my `bla.tex` document via `\includegraphics{foo.pdf}`. Say that `foo.pdf` is a colored document and that I need `bla.pdf` to be in gray levels. How can I do?

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What about using Ghostscript as external tool: gs -sOutputFile=output-filename -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dCompatibilityLevel=1.4 input-filename < /dev/null –  susis strolch Oct 18 '13 at 20:59
Thanks, but I'd rather rely on pdftex (no external tool). BTW, your command output an error `Error: /undefinedfilename in (sDEVICE=pdfwrite)`. –  cjorssen Oct 18 '13 at 21:09
@cjorssen: The option starts with a hyphen: `-sDEVICE=pdfwrite` –  Heiko Oberdiek Oct 18 '13 at 21:41
Indeed. Thanks. @susis strolch Would you mind turn you comment into an anwer as it seems to be the right way to do what I ask. –  cjorssen Oct 18 '13 at 22:11

``````gs -sOutputFile=output-filename -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dCompatibilityLevel=1.4 input-filename < /dev/null