How to Highlight Areas in a Large Scanned PDF Document
Question details
The user needs a way to highlight or mark specific visual regions, such as circuits, in an oversized scanned PDF without relying on OCR or text selection.
- Product
- WPS PDF
- Device & OS
- not provided
- Scenario
- Reviewing and marking up large scanned diagrams, blueprints, or circuit layouts where traditional text highlighting is unavailable.
- Observed behavior
- Standard text highlight tools cannot be used because the scanned document functions as an image layer and lacks selectable text.
Ensure your PDF editor supports drawing and shape annotations, as standard highlighting features require selectable text.
Use Shape Annotations to Outline and Highlight Areas
Since standard text highlighting requires selectable text, you can use drawing markups like the Polygon tool to manually trace and fill areas of interest on a scanned document.
Drawing markups act as visual overlays on top of the scanned image. By applying a semi-transparent fill color to a closed shape, you can effectively highlight diagrams, maps, or circuits without altering the underlying file.
Open your scanned PDF and navigate to the 'Comment' or 'Markup' tab on the top ribbon, then select the 'Polygon' tool from the shapes menu.
Click along the edges of the circuit or specific area you want to highlight. Connect the final point to the starting point to create a closed shape.
Click to select the newly drawn polygon annotation, then press 'Ctrl+E' on your keyboard to open the floating properties toolbar.
In the properties toolbar, choose a bright fill color (like yellow) and lower the opacity slider so that the scanned image beneath the shape remains clearly visible.
Easily Highlight and Annotate Any PDF with WPS Office
WPS Office provides a comprehensive suite of PDF markup features, including versatile shape annotations, freehand drawing, and adjustable opacity tools. This makes it incredibly simple to highlight non-text areas in complex scanned documents seamlessly.
- 1. Install WPS Office: Download and install WPS Office on your computer or mobile device.
- 2. Open the Scanned PDF: Launch the application and open your oversized scanned PDF document using the WPS PDF tool.
- 3. Navigate to the Comment Tab: Click on the 'Comment' tab located in the top menu bar to access the suite of markup and drawing tools.
- 4. Draw and Customize: Use the shapes tool to outline your desired area, then adjust the fill color and transparency via the floating properties menu to create a highlight effect.
Frequently Asked Questions
Why can't I use the standard highlight tool on my scanned PDF?
Standard highlight tools are designed to snap to selectable text. Because a scanned PDF is essentially a flat image, there is no underlying text to select unless you run an Optical Character Recognition (OCR) process first.
How do I make the shape fill transparent so I can see the diagram underneath?
After drawing the shape, select it and press Ctrl+E to open the properties toolbar. From there, locate the opacity or transparency slider and reduce it until the details of your underlying scanned image show through clearly.
Why shouldn't I just use OCR to highlight the circuits?
OCR (Optical Character Recognition) is optimized for recognizing letters and words. It generally struggles with non-standard visual layouts, blueprints, or complex circuit diagrams, making manual shape highlighting a far more accurate and efficient choice for visual markup.
Can I hide these shape highlights before printing the PDF?
Yes. Shape annotations sit on a markup layer. Depending on your PDF reader's print settings, you can choose to print 'Document Only' rather than 'Document and Markups', which will output the original scan without your drawn highlights.
