Frequently asked questions

Usually one of four reasons. The document was scanned from a faint original, so the "black" text is really mid-grey. The scanner captured grey paper, and the printer reproduces that grey faithfully. The PDF uses a very thin font, which a screen smooths out but a printer cannot. Or the printer itself is set to toner-save/draft. A screen is backlit and adds apparent contrast; paper does not, so anything already marginal on screen falls apart in print. See why PDFs print lighter than they look.

Upload the file above. DarkenMyPDF measures each page, works out how faint the ink is relative to the paper, and applies a tone curve that pushes the ink towards black while pushing the paper towards white. You can also drive it manually with the Text Darkness slider under Advanced settings.

Yes — that is the case it was built for. Scanned pages are rendered, measured, corrected for uneven lighting, re-toned and written back into a new PDF. Try Make Scanned PDF Darker.

Your screen emits light, so grey text on a light grey background still looks like solid contrast. Paper only reflects it. A 40% grey that reads clearly on a monitor prints as a washed-out grey, and toner-saving modes make it worse. Darkening the file before printing fixes the cause rather than fighting the printer.

Yes. Every page is measured and corrected on its own, so a document that mixes clean pages with faint scans is handled correctly rather than getting one blanket adjustment. The current limit is 100 pages per file.

Yes, on modern iPhone, iPad and Android browsers. Processing happens on the device, so a very large scan may take longer on a phone than on a laptop, and extremely large files may run out of memory — the tool tells you if that happens instead of failing silently.

No. Nothing is uploaded. The whole pipeline — reading, rendering, measuring, enhancing and writing the new PDF — runs inside your browser tab. There is no server that receives your document, so there is nothing to store, log or delete. Read the privacy policy for the specifics.

Never. The tool reads your file and writes a brand new one, saved with a new name such as `invoice-print-ready.pdf`. The file on your disk is untouched.

Yes. If a page is already solid black on clean white, Auto Print Enhance recognises that and applies almost nothing, so it does not degrade a good page. If a black-and-white page is faint, it gets the full correction.

Yes. There is no account, no email and no signup. Open the page, pick a file, download the result.

That is an explicit design goal. The tool uses a tone curve rather than a hard black/white threshold by default, so grey ink gets darker instead of disappearing. Coloured content — signatures, stamps, logos, highlighted rows — is darkened more gently and keeps its hue. If you do want a pure two-tone result, Black & White mode is available under Advanced settings.

On digital PDFs, yes. Pages made of real text are darkened by rewriting their colour instructions, so the text stays real text — sharp at any zoom, still selectable, still searchable, and the file stays small. Scanned pages are images to begin with, so those are enhanced as images.

The current limits are 50 MB and 100 pages. Because the work happens on your own device, the practical ceiling is really your device's memory; the limits exist so you get a clear message instead of a crashed tab.

Scanned pages are re-rendered at 150 DPI, which is the sweet spot for text on a home or office printer. Digital text pages are not rasterised at all, so they stay resolution-independent.