SumatraPDF Dark Mode Not Working: How to Fix It

If SumatraPDF dark mode is not working as expected, first identify what remains light. SumatraPDF can apply a dark theme to its tabs, menus, toolbar, window background, and other interface controls without turning the white pages inside a PDF dark. A setting may also fail to persist because you opened a different SumatraPDF installation, edited the wrong settings file, or saved that file incorrectly. The steps below separate these possibilities so you can fix the actual symptom without repeatedly reinstalling the application.

1. Confirm the Symptom With a Simple Document Test

Begin by determining whether the problem affects the application interface, the document itself, or both. This distinction matters because the application theme and document rendering are separate parts of the reading experience.

1.1 Test the interface theme without relying on a document

Open SumatraPDF and look at its menus, toolbar area, tabs, window background, and start page. Open the theme menu under Settings > Theme, then select Dark or Darker. The available capitalization can vary in displayed menus or settings text, but the relevant theme choices are light, dark, and darker.

Close the theme menu and inspect the interface. If the surrounding controls become dark while the open PDF page remains white, the theme is working. Stop changing the theme setting at this point. Your remaining issue is document color, not a failed application theme.

If none of the interface controls change, close and reopen SumatraPDF once. A restart is also useful after editing advanced settings manually. Success means that the application frame and controls use the selected dark appearance after reopening.

1.2 Compare a normal PDF with an EPUB

Use two uncomplicated test files if possible: a standard PDF with black text on a white page and a DRM-free EPUB that you know opens normally. Do not begin with a scanned PDF, protected publication, unusually designed comic, or file opened from a managed document system.

• Open the PDF and note whether only the interface changes.
• Open the EPUB and see whether its reading area responds differently.
• Return to the start page and confirm that the controls still use the chosen theme.

PDF pages generally contain fixed page graphics and explicit colors. EPUB content is usually reflowable and can be styled by a reader, although an EPUB may include its own colors and formatting. Different results between the two files therefore do not automatically indicate that SumatraPDF is broken.

If the dark interface appears consistently with both test files, the theme has succeeded. Continue only if your goal is to alter document colors or if the theme disappears after restarting.

2. Check the Theme and Document Setting Directly Related to the Problem

2.1 Use Settings > Theme before Advanced Options

For a normal theme change, use Settings > Theme first. Select Dark or Darker, depending on how dark you want the interface to appear. Select Light if you want to verify that switching works in both directions.

A successful test produces an obvious change in menus, controls, and the area surrounding the document. Once you can switch from light to dark and back again, stop troubleshooting the theme selector. Reinstalling SumatraPDF will not make a fixed-layout white PDF page automatically become dark.

2.2 Understand document background color versus interface controls

The theme controls the application appearance. It should not be treated as a universal promise to invert every document. A PDF can explicitly draw a white rectangle as its page background, place text inside images, use transparency, or contain scanned page images. Changing the surrounding reader interface does not rewrite those objects.

The visible area around a fixed page can also have a configurable background color. Changing that canvas or background may make the reading window more comfortable, but it does not necessarily change the page itself. If the page stays white while the area around it becomes dark, the setting has affected the viewer background successfully.

Be cautious with color-forcing or inversion options. Inversion can make photographs, diagrams, highlighted text, signatures, and accessibility colors look wrong. Always test with a copy of an ordinary file before deciding that a document-specific result represents an application failure.

2.3 Use Advanced Options only for supported settings

Settings > Advanced Options opens SumatraPDF's settings text file. This is useful when a menu selection does not persist or when you need to inspect the active configuration. It is not necessary for an ordinary menu-based theme change.

Look for the theme entry and confirm that its value corresponds to the intended light, dark, or darker choice. Preserve the existing formatting and use a value that SumatraPDF itself has written or that appears in the official settings documentation. Avoid pasting configuration blocks from old forum posts because setting names and accepted structures can change.

Save the file as plain text, close SumatraPDF completely, and open it again. Success means the selected theme remains active after the restart. If SumatraPDF rewrites the value or continues using another theme, you may be editing the wrong settings file or the file may not be writable.

3. Check the Active Copy, File Type, and Windows Context

3.1 Verify which SumatraPDF executable Windows opened

Windows can have an installed copy of SumatraPDF and one or more portable copies at the same time. A PDF file association, desktop shortcut, taskbar shortcut, or command launched by another program may open a different executable from the one you configured.

Perform this direct test:

1. Close every SumatraPDF window.
2. Open the exact SumatraPDF executable or shortcut whose theme you changed.
3. Confirm that its interface is dark.
4. Use that window's open command to load the test PDF.
5. Then double-click the same PDF in File Explorer and compare the result.

If double-clicking produces a differently themed window, the Windows file association probably points to another copy. Change the default PDF application through Windows settings or update the shortcut so it launches the intended executable. Success means opening the program directly and opening a PDF from File Explorer produce the same theme and behavior.

3.2 Separate format behavior from a global theme failure

SumatraPDF supports several document families, including PDF, EPUB, comic archives, CHM, DjVu, XPS, images, and other supported formats. These formats do not all render content in the same way. A fixed PDF page, an image-based comic, and reflowable EPUB text can respond differently to color-related settings.

If dark controls appear around a bright comic page or scanned PDF, the reader theme is functioning. The page is bright because its pixels or document objects are bright. Similarly, a publication can define its own text and background styles. Test a normal PDF and a simple EPUB before attributing the behavior to the entire application.

If only one file fails to display normally, try another file of the same type. A single damaged, unusually encoded, protected, or permission-limited document is a source-document problem rather than evidence that SumatraPDF dark mode is not working globally. Do not attempt to bypass DRM or remove document restrictions.

3.3 Know when external tools are unrelated

Ghostscript, printer drivers, codecs, shell preview handlers, and conversion tools can matter for particular workflows, but they do not normally control the color of SumatraPDF's menus or toolbar. Do not install Ghostscript or replace a printer driver merely because the application interface remains light.

Investigate external components only when the symptom occurs during a related action. For example, a printout that ignores an on-screen appearance points toward print settings or the printer driver. A file converted by another program may contain permanently embedded light colors. An image or uncommon format that fails while standard PDFs work may involve that file or its decoding path.

The stopping rule is simple: if the menu and window theme changes correctly and ordinary files open, external tools are not the cause of the theme problem.

4. Inspect or Reset SumatraPDF-settings.txt Safely

4.1 Find the settings file actually in use

An installed SumatraPDF copy commonly keeps its user settings in the SumatraPDF folder under the current Windows user's local application data. A portable copy commonly keeps its settings beside the executable when that location is writable. This difference is a frequent reason a manual edit appears to do nothing.

The installed location is typically:

%LOCALAPPDATA%\SumatraPDF\SumatraPDF-settings.txt

For a portable copy, check the folder containing SumatraPDF.exe. The safest method is to launch the copy you intend to use and choose Settings > Advanced Options. The file opened from that command is the configuration associated with that running copy.

If the executable is in a protected folder or on read-only media, the portable program may be unable to save beside itself. Move a portable test copy to a normal writable folder owned by your Windows account rather than changing broad folder permissions.

4.2 Save the file without changing its type

When editing SumatraPDF-settings.txt, keep it as a plain-text file with the same name. A common mistake is saving it as SumatraPDF-settings.txt.txt because Windows hides known file extensions. Another is saving a separate copy in Documents while the application continues reading the original file.

1. Open Advanced Options from the SumatraPDF instance being tested.
2. Change only the relevant theme value.
3. Use Save, not Save As, unless you have verified the exact destination and filename.
4. Close all SumatraPDF windows.
5. Reopen the same executable and inspect the theme.

Success means the value remains in the file and the interface retains that theme after a restart. Once this happens, stop editing the settings file.

4.3 Reset without permanently deleting preferences

If the file looks malformed or the selected theme will not persist, close SumatraPDF and create a backup. Rename SumatraPDF-settings.txt to a recognizable name such as SumatraPDF-settings-backup.txt. Do not delete it yet.

Reopen SumatraPDF so it can create a fresh configuration, then select the dark theme from the menu. If the fresh configuration works, the old file likely contained a conflicting or invalid setting. Reapply only the preferences you need rather than copying the entire old file over the new one.

If the reset makes no difference, restore the backup after closing SumatraPDF. This avoids losing reading preferences while you investigate the active executable or document behavior.

5. Run a Clean Temporary Test Before Reinstalling

A clean test answers whether SumatraPDF itself can apply the theme without destroying your current configuration. Download the current release only from the official SumatraPDF website, and use a portable build in a new writable folder if one is available for your system.

1. Close all existing SumatraPDF windows.
2. Create a new folder in a writable location, such as a folder inside Downloads or Documents.
3. Place the clean portable files there without copying your old settings file.
4. Launch that executable directly.
5. Select Settings > Theme > Dark or Darker.
6. Open one normal PDF and one simple EPUB.
7. Close and reopen the same executable to test persistence.

If the clean copy keeps a dark interface, SumatraPDF's theme feature is working. The original problem is likely an old configuration, an unwritable settings location, a shortcut to another executable, or a file association that launches another copy. Reinstalling is unnecessary until those causes have been excluded.

If both clean and existing copies show dark controls but white PDF pages, there is no application-theme failure to repair. Your expectation concerns page recoloring, which is separate from the interface theme and may not be appropriate or available for every document format.

6. Quick Fix Checklist

• Choose Settings > Theme > Dark or Darker.
• Confirm whether the controls or only the document page remain light.
• Restart the same SumatraPDF executable once after changing advanced settings.
• Test with an ordinary PDF and a simple DRM-free EPUB.
• Open Advanced Options from the running copy to find its active settings file.
• Ensure SumatraPDF-settings.txt remains plain text with the correct filename.
• Check whether Windows file associations launch a different installed or portable copy.
• Rename the settings file for a reversible reset instead of deleting it.
• Run a clean portable test from a writable folder before reinstalling.
• Stop troubleshooting when the interface is dark and the preference survives a restart.

7. Frequently Asked Questions

7.1 Why is my PDF page still white in SumatraPDF dark mode?

The theme can darken the application interface without recoloring fixed content inside a PDF. A PDF page may explicitly contain a white background, black text, photographs, or scanned pixels. If the menus, tabs, and area around the page are dark, the application theme is working.

7.2 What is the difference between Dark and Darker?

Both are theme choices intended to provide a dark application appearance, while Darker uses a more strongly darkened presentation. Choose whichever is comfortable and verify it by looking at the interface controls. Neither choice should be assumed to invert every page in every supported document format.

7.3 Why does the theme reset whenever I reopen SumatraPDF?

The most likely causes are an unwritable settings location, editing the wrong SumatraPDF-settings.txt file, launching another installed or portable copy, or a malformed settings file. Open Advanced Options from the active window, save the correct file, close every instance, and relaunch that same executable.

7.4 Where is SumatraPDF-settings.txt located?

An installed copy typically uses %LOCALAPPDATA%\SumatraPDF\SumatraPDF-settings.txt. A portable copy commonly stores the file next to its executable when the folder is writable. Use Settings > Advanced Options from the running instance to avoid guessing which file is active.

7.5 Should I reinstall SumatraPDF to fix dark mode?

Not initially. First test the theme menu, restart the program, verify the executable opened by Windows, back up and reset the active settings file, and run a clean portable copy. Reinstallation is reasonable only if a clean test also fails to change the interface and you have confirmed that you are launching the expected copy.

7.6 Why does an EPUB look dark while a PDF stays white?

EPUB content is commonly reflowable and can respond to reader styling, while a PDF usually describes a fixed page with explicit graphics and colors. This difference is expected. If both files open and the interface uses the selected theme, SumatraPDF is generally functioning normally.