How to convert a PDF to grayscale from command line avoiding to be rasterized?

Question

I\'m trying to convert to grayscale this PDF: https://dl.dropboxusercontent.com/u/10351891/page-27.pdf

Ghostscript (v 9.10) with pdfwrite Device fails with a \"Unabl

Answer 1

very late response, but the following command should work :

convert -colorspace GRAY input.pdf input_gray.pdf