Drawing attention to a clause, a figure or a date in a PDF before sending it on is a common need. This draws a semi-transparent coloured band at a position you set, exactly like a highlighter pen — the text underneath stays fully readable and selectable.
Your file never leaves your device. It is read and edited by JavaScript running in this tab. Nothing is uploaded or stored.
Enter your details
Result
Fill in the fields above and your result will appear here.
What the Highlight PDF does
The band is a translucent rectangle drawn on top of the page. Because it is semi-transparent rather than opaque, the content beneath shows through and remains selectable, which is what distinguishes a highlight from a redaction.
Positioning is numeric — this does not detect where words are on the page. On A4 body text, a height of 3–4% covers roughly one line, and adjusting the vertical percentage in small steps moves it line by line.
How to use this tool
- Select your PDF and use the thumbnail to judge roughly where the band should sit.
- Set the position and size as percentages. Start with 4% height for a single line of text.
- Choose a colour and opacity — 40% yellow is the familiar highlighter look.
- Tick the pages to mark, then press Add highlight and adjust if the band is off.
How the band is drawn
A translucent rectangle, positioned from the bottom-left:
x = page width × (across % ÷ 100)
y = page height × (up % ÷ 100)
width = page width × (width % ÷ 100)
height = page height × (height % ÷ 100)
Drawn with the chosen colour and opacity ON TOP of the page.
Because it is semi-transparent, the text underneath stays
visible and selectable — this is a highlight, not a redaction.
Worked example
Example: marking a clause
| Position | 12% across, 62% up |
| Size | 76% wide, 3.5% tall |
| Style | yellow at 40% opacity |
| Result | one line of text highlighted, still readable |
On A4, 1% of page height is about 3 mm, so a 3.5% band covers a standard line of body text with a little margin.
What your result means
Text stays readable and selectable underneath. That is the difference between highlighting and covering something up.
Opacity above about 60% starts to obscure the text. Keep it at 40% or below for normal highlighting.
The same band appears on every selected page, at the same position — useful for marking a column, less so for marking different lines.
Important considerations
- This does not find text. Position the band by eye from the thumbnail and expect to adjust once.
- On A4, roughly 1% of page height is 3 mm, which makes it easy to step down line by line.
- To mark several separate lines, run the tool repeatedly on the output.
- A highlight is not a redaction — the content underneath is fully intact. Use redaction to remove content.
- A PDF reader's own highlighter creates a proper annotation object that can be removed; this draws directly onto the page and is permanent.
Limitations of this tool
- Password-protected PDFs cannot be opened without the password.
- Processing happens in your device's memory, so very large documents can be slow.
- Existing text cannot be edited or removed — these tools add content on top of the page.
- The band is positioned numerically — the tool cannot detect where specific words are.
- One band per pass; run again on the output to add more.
- This draws on the page rather than creating a removable PDF annotation.
Frequently asked questions
Can I highlight specific words automatically?
No. The tool draws a band at coordinates you set; it does not search for text. Use the thumbnail to position it and adjust once if needed.
Will the text underneath still be readable?
Yes. The band is semi-transparent, so at 40% opacity the text shows through clearly and remains selectable.
Can the highlight be removed later?
Not from the output — it is drawn onto the page. A PDF reader's own highlighter creates a removable annotation instead; keep your original if you may want it clean.
How tall should the band be?
About 3–4% of page height covers one line of body text on A4. Increase it to cover a paragraph.