When do you need a grayscale PDF?
When you're about to print a color file on a black-and-white laser printer at the office or library and want to see beforehand how the colors will turn out in gray. Or when an office asks for a "black and white" copy of a document you scanned in color, or you want to save color ink at home when printing lessons or worksheets.
How the tool works
The tool doesn't change color values inside the file. Instead it redraws each page as an image: it opens the page with PDF.js, renders it at double resolution (2x), turns every pixel into a gray level based on its brightness, and saves the page as an image in a new PDF with the same page sizes as the original. The "Conversion Mode" menu has two choices:
- Smooth Grayscale (default): keeps every shade of gray. Good for photos and charts.
- Pure Black & White: every pixel is either black ink or white paper. Light backgrounds turn white, while dark text, coloured text even when it is light (such as yellow or light green) and table lines turn black so they aren't lost. Good for text pages and faded scans, but colour photos become black patches. Pages are stored as PNG, so letter edges stay sharp and the file is much smaller than in grayscale mode.
How to convert a PDF to grayscale
- 1Choose a PDF or drag it onto the upload box.
- 2Under "Conversion Mode", pick "Smooth Grayscale" or "Pure Black & White".
- 3Click "Convert to Grayscale Now" and wait for every page; the status line shows which page is being converted.
- 4Click "Preview Result", then "Download Result". The file keeps its name with
_grayscaleadded.
What happens to file size and text?
Since pages become images, the outcome depends on the file. In our tests, a 6-page text report of about 5 KB grew to roughly 1.9 MB, while a 6-page uncompressed color scan of about 60 MB shrank to around 3 MB. If your goal is a lighter file, use Compress PDF, and see the best PDF compression methods for why the two differ.
Limitations
- Text becomes part of an image: it can't be selected, copied or searched. Getting it back requires OCR (optical character recognition), which this tool doesn't do.
- Links, bookmarks and form fields aren't carried over. In our test a ticked checkbox in a form came out empty, so if your file is a form, flatten it first with Flatten PDF.
- A file with a password or permission restrictions isn't converted; a message asks you to unlock it first and try again with the open copy.
- Long files take time and memory, and the practical limit depends on your device.
Where is the processing done?
Rendering the pages and converting their colors happen in your browser, using your device's memory. There's no upload step, and nothing from the file reaches us.
Grayscale PDF: frequently asked questions
Why can't I copy the text anymore?
Because every page was redrawn as a gray image. Keep the original if you still need the text.
Do page sizes change?
No. Each page in the new file has the same width and height as the original page.
Which mode should I use for a faded scan?
Try "Pure Black & White", which raises contrast. If the page comes out too dark, for example because the scanned paper is grey, go back to Smooth Grayscale.
Do I need this just to print in black and white?
Not always: most printers offer a "monochrome" or "grayscale" option in the print dialog. The tool helps when you actually need a gray file to send or check. We measured when converting saves ink and when it doesn't in converting PDF to black and white for printing.