When Grayscale Saves You Money
Office colour cartridges are far more expensive per page than black. Many documents — reports, contracts, statements, lecture notes — carry colour only in headers, logos or charts that read perfectly well in grey. Converting to grayscale before printing forces the printer to use only the black cartridge, which can cut per-page cost dramatically across a large print run, and produces a consistent look when you are combining material from many sources.
Grayscale also helps when scanning or archiving. A monochrome page is smaller than a full-colour one, and removing colour noise from a scan often makes the text easier to read and OCR. The conversion here uses a luminance formula (weighting red, green and blue the way the human eye perceives brightness) so the result looks natural rather than washed out.
How the Conversion Works Locally
Each page is rendered to a canvas, every pixel is recomputed to its grey equivalent, and the desaturated pages are reassembled into a new PDF — all inside your browser. Because the page is flattened to an image, any hidden colour data is genuinely gone, and the file never leaves your device.