If you cannot highlight text in a PDF, the file usually does not contain real text. Most often the PDF is scanned or saved as images. In some cases, highlighting is blocked by security settings. The most common fix is OCR, which turns images into real text.
What This Problem Looks Like
Highlighting does not work when:
- •The highlight tool is grayed out
- •You try to mark text, but nothing happens
- •You cannot select text at all
- •Ctrl+F often does not work
- •Highlighting works in other PDFs, but not this one
Important:
Highlighting only works on real text.
If the PDF only contains images, highlighting is not possible.
This page only covers highlighting not working.
If text cannot be selected or copied at all, that is a different issue.
Fix Highlight Text in PDF Not Working
Common Reasons Highlighting Doesn’t Work
Most Common: The PDF Is Scanned
Many PDFs are just pictures of pages.
This means:
- •text looks readable
- •but it is only an image
- •highlighting does not work
OCR is required to fix this.
PDF Was Saved as Images
Some PDFs are created incorrectly:
- •screenshots saved as PDF
- •“Print to PDF” used instead of export
- •design files flattened
These PDFs contain no real text.
Highlighting Is Blocked by Security
Some PDFs block:
- •text selection
- •copying
- •highlighting
If this is the case:
- •text may still be visible
- •but highlight tools are disabled
You need an unlocked version from the sender.
Text Layer Is Broken (Less Common)
Sometimes the PDF has text, but:
- •highlighting does not work
- •selection behaves strangely
- •only some apps can highlight
This can happen after bad OCR or file repairs.
Viewer Problem (Rare)
Some PDF viewers cannot highlight text properly.
If highlighting works in Adobe Reader but not in your browser, the viewer is the problem.
Quick Check (1–2 Minutes)
1Step: Try Selecting Text
Drag your mouse over the text.
- •selectable → text exists
- •not selectable → scanned or blocked
2Step: Try Ctrl+F
Search for a word you see.
- •found → text exists
- •not found → scanned PDF
3Step: Check Security
File → Properties → Security.
If text selection is restricted, highlighting is blocked.
4Step: Try Adobe Reader
If highlighting works there, your viewer is the issue.
How to Fix Highlighting
Best Fix: Use OCR
OCR turns images into real text.
With Adobe Acrobat:
- •Tools → Text Recognition
- •Run OCR
After this:
- •text can be selected
- •highlighting works
- •Ctrl+F works
Free Option: Online OCR Tools
If you don’t have Acrobat:
- •search “PDF OCR online”
- •upload the PDF
- •download the fixed file
Works best with clear scans.
If Highlighting Is Blocked
If the PDF is restricted:
- •you need the owner password
- •ask the sender for an unlocked version
Avoid tools that promise to remove protection without permission.
If You Created the PDF
To avoid this problem:
- •export directly to PDF
- •do not use screenshots
- •avoid “Print to PDF”
This keeps text highlightable.
When Highlighting Cannot Be Fixed
Highlighting may not work if:
- •the scan is very blurry
- •the file is locked and cannot be unlocked
- •the original document is unavailable
In these cases, the document must be recreated.
FAQs
Why is the highlight tool grayed out?
Because the PDF has no real text or is restricted.
Why can I see text but not highlight it?
Because the text is an image, not real text.
Why does highlighting work in some PDFs but not others?
Only PDFs with a text layer support highlighting.
Can I fix this for free?
Yes, with free online OCR tools.
Is a PDF broken if highlighting doesn’t work?
No. It is usually just scanned or restricted.