Convert a Color PDF to Monochrome


Be aware that this procedure will flattern vector images and text in the source PDF into images - the file size will grow in this situation.

pdftk input.pdf burst output "intermediate-%03d.pdf"

for i in intermediate-*.pdf; do
  convert -density 150 ${i} -monochrome -quality 100 -sharpen 0x1.0 ${i%.*}_mono.pdf

pdftk intermediate-*_mono.pdf output output.pdf

rm intermediate-*.pdf

Not Authorized

If ImageMagick / convert complains about being "not authorized", then edit /etc/ImageMagick-6/policy.xml:

  <!-- snip -->
  <policy domain="coder" rights="read|write" pattern="PDF" />
  <!-- snip -->
sed -re '/<policy /{/pattern="PDF"/{s/(rights)="[^"]+"/\1="read|write"/}}' \
  -i /etc/ImageMagick-6/policy.xml