Darken a PDF

How to darken a PDF

1. Choose your PDF in the box above, or drop it on the page. It is opened in your browser and never uploaded.
2. Wait while each page is measured and corrected. A multi-page file is processed page by page.
3. Drag the slider to compare the original with the darkened version.
4. If the result is too strong or too gentle, open Advanced settings and adjust Text Darkness. The file is re-processed with your change.
5. Download the new PDF. Your original file is not modified.

Darken a PDF free, without Adobe or a download

You do not need Adobe Acrobat, a desktop program or an account to darken a PDF. This opens in your browser tab, costs nothing and adds no watermark. Because the file is processed on your own device and never uploaded, it is also fine for private documents.

It suits the usual "my PDF is very light" and "my PDF is not dark enough" cases: a dim scan, a page whose text is pale grey, or a document that looks fine on screen but is too faint to read once printed. For paper, start with darkening a PDF for printing; for the printer-side checks, see why a PDF prints too light.

Why some PDFs come out faded in the first place

• The author set the text to a grey or a light colour. This is common in templates and exported design files, and it looks acceptable on a bright screen.
• The page is a scan or a photo taken with too little exposure, so the ink was captured as mid-grey instead of black.
• A thin or light-weight font was used, so the strokes are too fine to print solidly.
• The PDF is a copy of a copy: every generation of photocopying or re-saving lowers the contrast a little more.

Lines, outlines, images and stamps

On a page made of text and vector graphics, the colour of lines, borders and table rules is darkened along with the text, so a pale outline becomes a clear one. On a page that is a picture, such as a scanned drawing or a photographed outline, the whole picture is darkened as an image.

A faded stamp on a scan is lifted along with the rest of the page. Coloured stamps and signatures are darkened more gently so they keep their colour (the Keep colour option); a stamp that is almost the same shade as the paper cannot be fully recovered.

What "darker" actually means here

Every pixel on a page has a lightness value. On a healthy document the ink sits near 0 and the paper near 255, and your printer has an easy job. On a faint document the ink may sit at 150 and the paper at 220 — a gap of 70 out of 255 — and a printer, which cannot emit light, turns that narrow gap into mush.

The tool re-maps that range. The measured ink level becomes the new black point and the measured paper level becomes the new white point, with a gamma curve in between that favours the darker half. The result is ink that reads as ink and paper that reads as paper.

When darkening helps, and when it does not

• It helps a lot with scans of faint originals, photocopies of photocopies, and phone-camera "scans" of paper documents.
• It helps with digital PDFs whose author set the body text to a light grey — surprisingly common in templates and exported design files.
• It helps modestly with thin fonts: the Thicken thin text option outlines glyphs so they hold together in print.
• It cannot recover detail that was never captured. If a scan lost a signature entirely, no amount of contrast will bring it back.
• It will not fix a printer that is low on toner or set to draft mode. Check that first if every document prints faint.

Digital PDFs keep their real text

Most tools that "darken" a PDF quietly turn every page into a picture. That makes text blurry when zoomed, breaks copy and paste, breaks search, and can multiply the file size.

Here, a page made only of text and vector graphics is darkened by rewriting the colour instructions inside the page itself. The letters stay letters.

A page that contains any picture — a scan, a photograph, or even a logo — is treated as an image instead, and its text becomes part of that image. If you need text to stay selectable, check a page of the result before relying on it.