There may be situations that you would like to convert a coloured PDF document to black-and-while (monochrome or greyscale) for whatever reasons. One of the methods that can accomplish this is to use ImageMagick, free command-line software that can perform all sorts of functions related to images. The following examples are commands to convert a PDF in colour to black-and-white. Values in the parameters should be adjusted to suit the particular document in question to obtain optimal results. (Note: Ghostscript needs to be installed for working with PDFs)

“magick -density 600 in.pdf -threshold 60% -type bilevel -compress fax out.pdf”

“magick -density 600 in.pdf -level 10%,90% -type grayscale -depth 8 out.pdf”