2 cent tip
Convert a PDF to black and white version
The problem: you have a PDF with some coloured elements (like some logo, separation lines, etc…) but you need a PDF in B/W. The solution: you can print your file (with a B/W printer) and then scan it 
or, using GPL Ghostscript, run this command… gs -sDEVICE=pnggray -r150x150 -sOutputFile=output-%02d.png Read more…