How to Fix Cannot Highlight Text in a Scanned PDF
Question details
Users are unable to use the highlight tool to select or emphasize individual words within a PDF document.
- Product
- PDF Editor
- Device & OS
- not provided
- Scenario
- Attempting to highlight, select, or search for specific text segments in a PDF document created from a physical scanner.
- Observed behavior
- The highlight tool is active, but it either acts as a freehand drawing pen or does nothing at all, failing to snap to individual words or paragraphs.
Verify whether your PDF is a flattened image by pressing Ctrl+F (or Cmd+F on Mac) and searching for a visible word on the page. If the search turns up empty, your document lacks a searchable text layer.
Convert the Scanned Image to Searchable Text using OCR
By using Optical Character Recognition (OCR), you can extract actual text from the scanned image, allowing the highlight tool to recognize and snap to individual words.
A scanned PDF is essentially a photograph of a document. Because there is no underlying text layer, standard highlighting tools cannot identify where words begin and end. OCR technology analyzes the shapes in the image and converts them into selectable text.
Launch your PDF editor, open the scanned document, and navigate to the 'Tools' menu. Select 'OCR' or 'Recognize Text'.
Choose the correct document language in the prompt settings and click 'Start' or 'Recognize' to process the document.
Once the OCR process finishes, navigate back to the 'Comment' or 'Markup' toolbar. Select the Highlight tool, and you will now be able to drag your cursor to select and highlight individual words.
Use Drawing Markup Tools to Emphasize Areas
If you do not have access to an OCR tool, you can use built-in shape tools to manually draw a colored box over the areas you want to highlight.
Highlight Any Scanned PDF Easily with WPS Office
WPS PDF includes a powerful built-in OCR feature that instantly converts image-based, scanned PDFs into fully searchable and highlightable text. It is a lightweight, all-in-one PDF solution perfectly tailored for professional editing and annotation.
- 1. Open the PDF: Launch WPS Office and open your scanned PDF document.
- 2. Run OCR: Navigate to the 'Tools' tab and click on the 'OCR' button to recognize the text within the image.
- 3. Highlight Text: Go to the 'Comment' tab, select the 'Highlight' tool, and freely mark up the newly recognized text.
Frequently Asked Questions
How do I know if my PDF is an image-based scanned document?
Try to select a single word with your mouse cursor or use the 'Find' shortcut (Ctrl+F) to search for a word you clearly see on the page. If the cursor cannot grab text and the search comes up empty, your document is an image-based scanned PDF.
What does OCR stand for and why do I need it?
OCR stands for Optical Character Recognition. It is a technology that analyzes image files and recognizes the letters and words within them, converting them into machine-readable text that you can edit, search, copy, and highlight.
Can I highlight a scanned PDF without converting it to text?
Yes, you can visually highlight areas by using drawing tools like the 'Rectangle' or 'Area Highlight' tool found in the commenting section of most PDF editors. By setting a rectangle's fill to a transparent yellow, you can mimic a standard text highlighter without needing a text layer.
Why does the highlight tool only draw freehand lines instead of snapping to text?
When a PDF lacks an actual text layer (like a scanned photo of a physical document), the standard text highlight tool doesn't have words to anchor onto. Depending on your PDF reader, it will either do nothing or act like a freehand drawing pen.
