HowtoconvertaPDFtogreyscaleforprinting

Changing the file, not the print dialogue

Printing in black and white is a setting on the printer, which the print shop's counter does not see and the next person to open the file does not inherit. Converting the document makes it greyscale wherever it goes.

That is the difference worth understanding: one is an instruction to a machine, the other is a property of the document.

What it does to size

Colour information is discarded and pages are re-encoded, so image-heavy documents often shrink noticeably. Text-only files may barely change, because there was little colour data to remove.

The trade is the same one compression makes: pages are re-rendered, so the text layer does not survive. Keep the original.

Check the contrast before you commit

Colours that are clearly distinct in a chart can converge into the same grey. A legend with red and green lines becomes two identical grey lines. Look at any chart in the converted file before sending it to print — and if it fails, fix the source document's colours rather than the PDF.