How to Highlight in PDF
Learn how to highlight in a PDF, how to choose the right highlight color, and what to do if the file is read only or flattened.
How to Highlight in PDF (Quick Answer)
You can highlight in a PDF by using a PDF reader or editor that supports annotation tools.
The normal workflow is simple:
- Open the PDF
- Select the highlight tool
- Drag across the text you want to mark
- Save the file
That works best when the PDF contains real selectable text.
Highlighting Is an Annotation
Highlighting is usually not part of the original document content.
It is an annotation, which means you are marking the page without changing the underlying text.
That makes it useful for:
- Study notes
- Review comments
- Legal or contract review
- Shared feedback
It is a fast way to mark important text without rewriting the page.
Pick the Right Color
The highlight color matters more than people think.
Choose a color that:
- Stands out enough to be visible
- Does not hide the text underneath
- Fits the purpose of the markup
- Prints well if the file will be printed
Yellow is common, but other colors can help organize different kinds of notes.
What If the Text Cannot Be Selected?
If you cannot select the text, the PDF may be scanned, flattened, or image-based.
In that case:
- OCR may be needed first
- You may need to use a comment or shape tool instead
- The document may need to be converted before you can mark text normally
If the file is just an image, the highlight tool may not behave the way you expect.
Best Practice Summary
If you want the short version:
- Use a PDF tool with annotation support
- Select the highlight tool and drag over the text
- Pick a color that stays readable
- Use OCR if the file is scanned
- Save a copy after highlighting
That is the simplest way to highlight in a PDF.
FAQ
Can I highlight any PDF?
Not always. Scanned or flattened PDFs may not support normal text highlighting.
Does highlighting change the text?
No. It usually marks the text without editing it.
Can I change highlight colors later?
Often yes, if the highlight is still an annotation.
Is highlighting the same as redaction?
No. Highlighting marks text, while redaction removes or hides it.
Should I save a copy after highlighting?
Yes. That keeps the original unchanged.
Can I highlight in a browser viewer?
Some browser viewers support it, but not all do.