Tool for PDF conversion to black and white [closed]

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Is there a freely available (preferably open source) tool or library for PDF conversion to black and white?

Some customers want to print generated PDF documents in B&W to save toner. Unfortunately I cannot generate PDF in B&W directly, since we are merging two PDF pages together, one being official not available in B&W.

Update: To be more specific, I am looking for automatic solution, i.e. tool that is callable from a program.

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Having seen Viliam's insisting on wanting "Black and White", not "Grayscale" I'm still offering this solution to convert PDF files to grayscale. Because I think that would perfectly fullfil the requirement to "save color toner" and make use of black toner only.

Use Ghostscript (the most recently released version is 9.05) with this command:

 gs \
   -o black+white.pdf \
   -sDEVICE=pdfwrite \
   -dPDFSETTINGS=/prepress \
   -sColorConversionStrategy=Gray \
   -sColorConversionStrategyForImages=Gray \
   -sProcessColorModel=DeviceGray \
   -dCompatibilityLevel=1.4 \
    /path/to/input.pdf

On Windows, use gswin32c.exe or gswin64c.exe instead of gs. Ghostscript meets Viliam's request for:

• freely available
• Open Source
• callable from a program

and it does the job.

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Update

If color conversion does not work as desired and if you see a message like "Unable to convert color space to Gray, reverting strategy to LeaveColorUnchanged" then...

1. your Ghostscript probably is a newer release from the 9.x version series, and
2. your source PDF likely uses an embedded ICC color profile

In this case add -dOverrideICC to the command line and see if it changes the result as desired.

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Try this website,

http://online.puzzleflow.com/process/all2gray

It worked for me.

Update

It has been made a payed website

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With PrimoPDF (http://www.primopdf.com/index.aspx) you should be able to set to generate a "Black & White" pdf.

"Printing Preferences" -> "Paper/Quality" tab, then you can choose between "Black & White" and "Color.

Regards
Thomas