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Darken a Scanned PDFin your browser
Scans are usually a photo of a bright white page, which is rough on the eyes after sunset. PDF Dark flips that — the background becomes a dark color you pick, the text becomes near-white, and you get a new PDF you can keep.
Why scanned PDFs are harder to read at night
Two things make scans different from regular PDFs, and most reader apps can't do much about either.
Scans are pure raster
- No text layer, no fonts, no styles to restyle
- PDF reader "dark mode" toggles do nothing — they only retheme text PDFs
- You're looking at a photo of a page, and the photo is white
And the background varies
- Yellowed paper, off-white book scans, gray shadows
- OS-level invert turns yellow into purple — even uglier than the original
- A real color flip needs to normalize the background first, then apply the theme
PDF Dark's brightness mapping pulls every shade of “light” to your single theme color — old yellow scans and crisp white scans end up the same calm dark.
What “darken” means here
Worth being upfront about this before you feed in a 400-page scan: the tool inverts the page rather than just dimming it.
✅ Great fit
You want a true dark-mode reading experience: dark page, light text, comfortable at night. You're fine with the visual style changing — you care about eye strain, not about printing the file later.
⚠️ Probably not what you want
You want to keep a white background and only make faded text blacker (a contrast-only tweak). For that, look for tools that advertise “PDF contrast enhancement” or “OCR-and-rethreshold” — they preserve the page style and just deepen the strokes.
Pick the right theme for scans
- OLED — deepest contrast, best on OLED phones for battery
- Midnight — calm blue-grey, easiest on the eyes for long reads
- Solarized — cool teal; nice on retina laptops
- Skip Sepia on yellow-tinted old scans — too much warm-on-warm
Try it on one of your scans
Drop the file on the home page and switch between OLED, Midnight, and the others to see what looks right on your screen. The download is a regular PDF you can email or sync like any other.
Open PDF Dark →More from the PDF Dark blog
Different angles on the same converter — pick the post that matches your scenario. The drop zone is at the top of every page.
PDF Dark Mode in Chrome
PDF Dark Mode in Firefox
Convert PDF to Dark Mode
How to Darken a PDF
Darken scanned PDF — FAQ
Will this make the original text darker, or invert the whole page?
PDF Dark inverts. The bright background of your scan becomes a dark color (your theme), and the dark text becomes near-white. The result reads like a true dark-mode page — much easier on the eyes at night than the original bright scan, but it does change the visual style. If you specifically want to keep a white background and only deepen faded text, use an OCR + contrast tool instead.
Which theme works best for scanned pages?
OLED (pure black) gives the highest contrast and is best on OLED phones for battery. Midnight (deep blue-grey) is the most comfortable for long sessions. Avoid Sepia for scans that already have yellow paper tones — the warm theme can blend into faded scans.
Does the scan need to be OCR'd first?
No. PDF Dark treats every page as an image, which is exactly what a scan is. You get the same darkening whether the PDF has hidden text or not. (You also won't gain selectable text — keep your original file for that.)
Is my scanned PDF uploaded anywhere?
No. Conversion happens entirely in your browser via the File API and a Web Worker. Open DevTools → Network and you'll see no upload during conversion. The PDF never leaves your device.
My scan is 300+ pages. Will this still work?
On a laptop, yes — we render and darken pages in chunks. On a phone, very large scans can stall when memory runs out. If that happens, split the PDF first (any free PDF splitter works) and darken the halves separately.
Will old yellowed paper still look yellowed after darkening?
No. The brightness-mapping algorithm pulls every page toward your chosen theme color, so yellowed paper, off-white scans, and pure white pages all end up the same dark background. That uniformity is one of the biggest reading wins for old book scans.
Is there a file size or page limit?
No hard limit. Everything runs locally, so the only limit is your device's memory. Hundreds of pages are fine on modern hardware.