SumatraPDF Highlight Tool Not Working: How to Fix It

When the SumatraPDF highlight tool is not working, the cause is usually one of four things: the document has no selectable text, the file format does not support PDF highlight annotations, the PDF restricts changes, or the SumatraPDF build or settings being used do not expose the expected annotation command. The fastest approach is to test highlighting in a simple text-based PDF before changing Windows settings, reinstalling software, or editing configuration files.

This guide focuses specifically on creating persistent highlight annotations. It does not cover the temporary highlighting SumatraPDF displays when you search for a word. Follow the tests in order, and stop as soon as highlighting works. That prevents unnecessary changes to a reader that may already be configured correctly.

1. Confirm the Symptom With a Simple PDF Test

Begin by separating a document problem from a SumatraPDF problem. Open a small PDF that you know contains ordinary computer-generated text, such as a document exported from Microsoft Word, LibreOffice, or a browser's print-to-PDF function.

1.1 Check whether the text is selectable

Drag the mouse across one sentence. Individual characters or words should become selected. You should be able to copy the selection and paste readable text into Notepad.

If the entire page behaves like one image, the PDF is probably a scan without a text layer. A highlight annotation is normally attached to text coordinates, so SumatraPDF cannot create a normal text highlight when it cannot identify the underlying characters.

For a scanned PDF, use a legitimate optical character recognition application to create a searchable text layer, provided you have permission to modify the document. Then reopen the resulting PDF and repeat the selection test. OCR accuracy varies, so verify that copied text matches the page before relying on annotations.

Success looks like this: dragging selects the exact words rather than the whole page or a rectangular image area. Once that works, try the available highlight command. If the highlight appears and survives a save-and-reopen test, stop troubleshooting.

1.2 Test a known-good text PDF

If text is selectable in the original document but highlighting still fails, test a second, uncomplicated PDF. Avoid a form, digitally signed agreement, protected statement, scanned book, portfolio, or unusually large technical drawing for this test.

1. Open a simple text-based PDF in SumatraPDF.
2. Select a short phrase with the mouse.
3. Look in the selection context menu and the application's menus for a highlight or annotation command.
4. Apply the highlight if the command is available.
5. Save the document or save an annotated copy when prompted.
6. Close the file, reopen the saved file, and confirm that the highlight remains.

If the test PDF works, SumatraPDF's basic annotation function is operating. Return to the original document and investigate its text layer, permissions, or structure. Do not reset the application merely because one PDF fails.

2. Check the Annotation Command and Document Format

SumatraPDF can open many kinds of content, but the ability to display a format does not mean it can write PDF-style highlight annotations into that format. This distinction is especially important for users who also read eBooks, comic archives, CHM, DjVu, XPS, and image files.

2.1 Confirm that the active file is a PDF

Persistent text highlighting should be tested with a PDF. A document may look like a PDF in the reader while actually being an EPUB, MOBI, CHM, DjVu, XPS, comic archive, or image. Check the filename and extension in File Explorer rather than judging by its appearance.

If highlighting works in a PDF but no equivalent command appears for another format, that is a format capability issue rather than a broken installation. Converting content may change layout, pagination, links, or accessibility, so only use a trusted conversion workflow when you own the material or have authorization to convert it.

Success looks like this: the active document is a text-based PDF, selectable words are visible, and a highlight-related command appears after selecting text or within the annotation controls.

2.2 Look for annotation commands after selecting text

Annotation controls can vary with the installed build and active document. Select text first, then inspect the right-click menu and application menus for a highlight or annotation action. If the command only appears after text selection, the earlier absence was contextual rather than a fault.

If no annotation command appears anywhere while a valid PDF is open, check which SumatraPDF executable and build you launched. Windows shortcuts and file associations sometimes open an older installed copy even when a newer portable copy is stored elsewhere.

• Open SumatraPDF directly, then check its About information.
• Use the Open command inside that same window to open the test PDF.
• Avoid double-clicking the PDF until you know which executable Windows associates with it.
• Compare the path of your installed and portable copies if both exist.

Do not assume that reinstalling one copy changes another portable copy. Each executable may use a different settings location or may not be the program receiving PDF files from File Explorer.

2.3 Distinguish annotations from search highlighting

Search-result highlighting is temporary. It marks matches while the Find feature is active and is not written into the PDF. An annotation highlight is deliberately applied to selected text and must be saved to persist.

If yellow or another colored shading appears only while searching, you have not created an annotation. Exit the Find interface, select the intended passage, and use the annotation command instead.

3. Check the Source PDF, Permissions, and Saving Behavior

If SumatraPDF can highlight the simple test document but not the original, concentrate on the original file. Its security rules, text encoding, storage location, or structure may be responsible.

3.1 Review PDF permissions without bypassing them

A PDF can include permissions that restrict commenting or document changes. SumatraPDF should not be expected to override restrictions set by the document owner. If annotation is prohibited, request an annotatable copy or permission from the publisher, employer, institution, or document owner.

You can also open the document's properties or security information in a trusted PDF application to see whether commenting or changes are allowed. Do not use tools that claim to remove restrictions without authorization.

Success looks like this: you receive an authorized, unrestricted copy and can apply and save a highlight normally. If the document remains restricted, stop changing SumatraPDF settings because they cannot legitimately resolve the permission policy.

3.2 Save the annotation to a writable location

A highlight that appears but disappears after closing usually indicates a saving problem, not a rendering problem. After creating the annotation, use the appropriate Save command and pay attention to any error or prompt.

Test with a copy stored in a normal writable folder such as Documents. Files opened directly from email attachments, temporary browser folders, read-only media, network shares, synchronized locations, or protected corporate folders may not be writable.

1. Copy the PDF to your Documents folder.
2. Right-click it in File Explorer and open Properties.
3. Check whether the file is marked read-only.
4. Open the copy from within the intended SumatraPDF executable.
5. Apply one highlight and save.
6. Close and reopen the exact saved copy.

If prompted to save under another name, choose a clear test name and verify that you reopen that file, not the untouched original. Avoid overwriting an important document until the workflow has been verified.

3.3 Understand the default highlight color

Highlight annotations commonly appear yellow by default. A highlight can seem missing if its color or opacity has been changed to something difficult to see against the page. Inspect the annotation's properties or annotation editor, where available, and choose a visible color.

Test on black text against a white page. If the annotation exists in the annotation list but is barely visible, the issue is appearance rather than creation. Restore a conventional yellow highlight or another high-contrast color, save, and reopen the document.

3.4 Know when external components are relevant

Codecs, Ghostscript, and printer drivers are not normally responsible for applying a highlight annotation to an ordinary PDF. They may matter in workflows involving image decoding, PostScript conversion, printing, or creating a new PDF through a virtual printer, but they should not be the first target for this symptom.

Only investigate those components if the failure occurs during conversion or printing rather than during text selection and annotation. For example, if you create a PDF through a printer driver and the resulting pages contain only images, that output may lack selectable text. The practical fix is to generate a text-based PDF using an export function that preserves text, not to change SumatraPDF's annotation settings.

4. Inspect SumatraPDF-settings.txt Safely

SumatraPDF stores preferences in a file commonly named SumatraPDF-settings.txt. Its location can differ between installed and portable use. Settings persistence matters when annotation controls, colors, or other behavior change between launches.

4.1 Verify that you are editing the active settings file

Do not search the entire computer and edit the first file with that name. An installed copy and a portable copy can have separate settings files. Changes made to an inactive file will have no effect and can create confusion.

Use SumatraPDF's own settings or advanced-options command, if available in your build, to open the active configuration. Otherwise, close SumatraPDF and identify the settings file associated with the executable you are testing. Portable mode commonly keeps application-related files near the portable executable, while an installed application generally uses the current Windows user's application data.

4.2 Back up before making changes

Close SumatraPDF, then copy the active settings file to a safe location. Give the backup a recognizable name such as SumatraPDF-settings-backup.txt. This preserves reading preferences, recent-file information, display choices, and any annotation appearance settings stored there.

When reviewing the file, avoid pasting configuration blocks copied from random forum posts. Available keys can change, and an invalid or obsolete line may be ignored. If the current file contains annotation color settings, check for an unusual highlight color or value. Make the smallest possible change and retain the original formatting.

Success looks like this: after reopening SumatraPDF, the chosen annotation appearance remains consistent, and a new highlight is visible after saving and reopening the PDF. If behavior does not change, restore the backup and proceed to a clean test.

4.3 Reset only when persistence appears broken

A reset is reasonable when SumatraPDF repeatedly forgets settings, the configuration file appears damaged, or the feature works under another Windows account or clean portable copy. It is not the correct first response when only one scanned or restricted PDF fails.

With SumatraPDF closed, rename the active settings file rather than deleting it. For example, append .old to the filename. Launch the program and let it create a fresh configuration. Open the known-good test PDF and try one highlight.

If highlighting works with fresh settings, the old configuration was likely involved. Reapply preferences gradually instead of restoring the entire old file. If it still fails, close the application and restore the original file if desired.

5. Run a Clean Temporary Test

A clean test helps distinguish application state from document state without immediately uninstalling anything. It is particularly useful when the computer has both installed and portable copies.

5.1 Test with a separate official copy

Download SumatraPDF only from its official website. Use a separate folder for a legitimate portable copy if that option is offered. Do not place it over the existing installation or copy old settings into it.

1. Close all SumatraPDF windows.
2. Launch the clean copy directly from its folder.
3. Open the simple text PDF through the application's Open command.
4. Select a short sentence.
5. Apply the available highlight annotation command.
6. Save to a new filename in Documents.
7. Close and reopen the saved copy.

If this succeeds, the original executable, shortcut, association, or settings environment is the likely source. You can continue using the clean copy or carefully repair the original setup. If it fails with multiple known-good text PDFs, verify annotation command availability in the official documentation before reinstalling.

5.2 Correct the Windows file association only if needed

A file association does not control whether PDF text can be highlighted, but it controls which program opens when you double-click a PDF. Correct it when direct opening in the tested SumatraPDF copy works but double-clicking launches another copy or another reader.

In Windows, use the Open with interface or Default apps settings to select the intended SumatraPDF executable. Then double-click the test PDF and confirm through the application's About information that the expected copy opened.

Success looks like this: direct opening and double-click opening produce the same annotation controls and saving behavior. Once they match, stop changing Windows defaults.

6. Quick Fix Checklist

• Confirm that the file is a PDF, not an eBook, image, CHM, DjVu, or XPS file.
• Drag across a sentence and verify that individual words can be selected.
• Copy the selection into Notepad to confirm that a real text layer exists.
• Test a simple PDF exported from a word processor.
• Select text before looking for the highlight or annotation command.
• Do not confuse temporary search matches with saved highlight annotations.
• Check whether PDF permissions allow comments or document changes.
• Save a test copy in a writable local folder such as Documents.
• Close and reopen the saved copy to verify persistence.
• Use a visible highlight color, normally yellow or another contrasting color.
• Confirm which installed or portable SumatraPDF executable is running.
• Back up SumatraPDF-settings.txt before editing or resetting it.
• Run a clean temporary test before reinstalling the application.
• Investigate printer drivers, Ghostscript, or codecs only when conversion or printing is involved.

7. Frequently Asked Questions

7.1 Why can I see the words but not select them?

The page may be a scanned image. Humans can read the pictured words, but the PDF may contain no machine-readable text layer. Run authorized OCR with a trusted application, then verify the result by copying a sentence into Notepad.

7.2 Why is the highlight command missing?

The active file may not be a PDF, no text may be selected, or the SumatraPDF copy in use may not expose the expected annotation functionality. Test a selectable text PDF, select words first, and check the context and application menus. Also confirm that Windows did not open an older or different executable.

7.3 Why does the highlight disappear after I close the PDF?

The annotation was probably not saved, the source file was not writable, or you reopened the original instead of the annotated copy. Save a copy in Documents, close it, and reopen that exact filename. A persistent colored highlight confirms success.

7.4 Can SumatraPDF highlight text in EPUB, CHM, DjVu, or XPS files?

Do not assume that PDF annotation tools apply to every format SumatraPDF can display. Test persistent highlighting in a PDF. If the command is unavailable for another format, use that format's supported note-taking workflow or an authorized tool designed for it.

7.5 Will reinstalling SumatraPDF fix highlighting?

Only sometimes. Reinstallation will not add a text layer to a scan, change PDF permissions, or make a read-only folder writable. A clean portable test is more informative because it isolates the executable and settings without immediately disturbing your current setup.

7.6 When should I stop troubleshooting?

Stop when a highlight can be applied to selectable text, saved, and seen again after reopening the document. If a simple PDF works but one source document does not, focus only on that document's text layer, permissions, or structure. If the document owner prohibits annotation, request an authorized copy rather than attempting to bypass the restriction.