Printing in colour costs more, and many printers in offices, schools and print shops charge per colour page or run out of colour ink at the worst moment. Some portals and examiners also ask for documents in black and white, and a colourful scan of a certificate or ID card can look messy on paper. Grayscale PDF turns every page into shades of grey in one step, so the document prints cleanly on any printer and looks the same everywhere.
There are two ways to do it. Keep text is the default and the right choice for most files. Every colour on the page becomes the grey of the same brightness, while text, lines and shapes stay exactly what they were: sharp at any zoom, searchable and copyable. Dark blue text stays dark, a light yellow highlight stays light, so nothing that was readable becomes unreadable. The file stays about the same size.
Turn pages into images is for cases where grey on screen is not enough. Some print shops and document checks look inside the file and treat any colour data as a colour page. This option draws each page at 150 dots per inch, turns every pixel grey and rebuilds the PDF from those grey pictures, so no colour is left anywhere. The trade-off is that text becomes part of an image: it prints well but can no longer be selected or searched, unless you run OCR PDF on the result.
The conversion runs in your browser on this device, and your file is never uploaded. That makes it safe for mark sheets, bank letters, medical reports and anything else you would rather not send to a stranger’s server. There is nothing to install and no account to create.
If the goal is a smaller file, follow up with Compress PDF; for a strict size limit, Compress to exact KB. To get only certain pages in black and white, first save them with Extract pages. And if you need the pages as images rather than a PDF, PDF to JPG is the quicker route.