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PDF Dark Mode in Sumatra PDFThe i Key, the Settings.txt Fix — and What Both Miss

Unlike Chrome or Adobe, Sumatra actually ships with two ways to darken a page. Here's exactly how they work, and where they fall short.

By PDF Dark TeamUpdated July 21, 20268 min read

Sumatra's two built-in dark mode tricks

Credit where it's due: Sumatra PDF gives you more than most readers do out of the box. Both options are real — and both have a catch.

The i key — instant, but it doesn't stick

With a PDF open in Sumatra, press i on your keyboard and the whole document inverts on the spot — background black, text white. It's the quickest dark mode of any PDF viewer we've covered. The catch: Sumatra doesn't remember the setting per file. Close the document and open it again — or open a different PDF — and it's back to white until you press i again.

Editing SumatraPDF-settings.txt — permanent, but technical

For a fix that survives closing the app, go to Settings → Advanced Options. This opens a plain text file, SumatraPDF-settings.txt. Inside, look for the FixedPageUI and EbookUI sections and change TextColor and BackgroundColor to hex values — for example eeeeee for text and 1a1a1a for the background. Save it, and every PDF opens with that color scheme from then on — no more repeated key presses. The catch: it's a manual text-file edit with hex color codes, which is comfortable territory for a lot of Sumatra users but a real barrier for anyone who doesn't want to hand-edit a config file.

Both methods share the same two blind spots

  • Images can come out wrong. Both the i shortcut and the settings.txt colors invert the whole rendered page, and photos or images with transparent backgrounds often end up looking off — a complaint that comes up on Sumatra's own forum.
  • It's tied to this one Windows PC. Sumatra PDF is Windows-only. Neither the shortcut nor the settings file follows the document to your phone, a Mac, or a browser — open the same PDF anywhere else and you're looking at a white page again.

What PDF Dark does differently

  • Convert once and the file itself is dark — no shortcut to repeat, no settings file to edit
  • Photos and images are detected and kept in their original colors, so nothing turns into a negative
  • The resulting PDF stays dark in Sumatra, on your phone, on a Mac, or in any browser — not just this one PC
  • Runs entirely in your browser tab — your file never leaves your device

Using PDF Dark instead of the i key or settings.txt

Open the PDF Dark converter in any browser, drag in the file, pick a theme, and download. No i key to remember, no settings.txt to edit — and unlike Sumatra's inversion, images are detected and kept in their original colors automatically.

It's a more deliberate process than a blanket invert — text gets recolored as vector data, and each image is evaluated on its own before the tool decides whether to touch it. The full technical writeup is here. The file it produces opens dark in Sumatra, on your phone, a Mac, or a different Windows machine, because the color change is baked into the file itself. Just want to read something once without saving a copy? Use the dark mode PDF reader instead.

Works in any modern browser on Windows, macOS, Linux, or a phone — you don't need Sumatra PDF installed to use it, and the file it produces still opens correctly in Sumatra afterward.

Ready for a PDF that's dark without pressing i every time?

3 steps, no settings.txt, no repeating a shortcut per file

Convert once and the dark theme is part of the file — open it in Sumatra, on your phone, or anywhere else and it stays dark.

Convert a PDF to dark mode →

Just want to read one now? Open the dark mode reader instead.

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Do You Need a PDF Dark Mode Extension?

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PDF Dark Mode on Mac

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PDF Dark Mode on Android

Android's default PDF viewers still don't have a real dark mode, and screen-invert flips everything negative. Convert once, read dark anywhere.

PDF Dark Mode on iPad & iPhone

iOS 26 finally added a Dark Background toggle for PDFs in Files and Books. Here's what it fixes — and what it still doesn't.

PDF Readers with Dark Mode, Compared

Acrobat, Foxit, Sumatra, Preview, Chrome, Edge, Firefox, mobile apps, extensions — which ones really darken the page, side by side.

Sumatra PDF dark mode FAQ

Does Sumatra PDF have a dark mode?

Sort of — and it's better equipped than most PDF viewers here. Sumatra ships with a keyboard shortcut that inverts page colors on the spot, plus a settings file you can edit for a permanent custom color scheme. Neither is a one-click "dark mode" toggle in the settings menu, but both are real, built-in options.

How do I invert colors in Sumatra PDF?

Open a PDF, then press the i key on your keyboard. Sumatra immediately inverts the current document — background goes black, text goes white. It's the fastest way to get a dark page, but it only applies to that viewing session: close the file and reopen it, and you'll need to press i again.

How do I make Sumatra's dark colors stick permanently?

Go to Settings → Advanced Options. This opens a text file called SumatraPDF-settings.txt. Inside it, find the FixedPageUI and EbookUI sections and change the TextColor and BackgroundColor values to hex colors — for example TextColor eeeeee (light gray) and BackgroundColor 1a1a1a (near-black). Save the file and every PDF you open afterward uses that color scheme automatically, no more pressing i.

Why do images look strange after pressing i or editing settings.txt?

Both methods are a straight color inversion applied to the whole rendered page, images included. Photos and especially images with transparent backgrounds can come out looking wrong — this is a known complaint on Sumatra's own forum. There's no way to tell Sumatra "invert the text but leave photos alone."

Will this work on my phone or on a Mac?

No. Sumatra PDF is Windows-only, so the i shortcut and the settings.txt edit only affect PDFs opened in Sumatra on that specific Windows machine. Open the same file on your phone, on a Mac, or in a browser, and you're back to a white page — you'd have to solve dark mode separately on every device.

Is my PDF uploaded anywhere when I use PDF Dark?

No. The conversion runs entirely in your browser tab via the File API and a Web Worker — nothing is sent to a server. You can confirm this yourself by opening DevTools → Network while converting a file.