Highlight text in a PDF
Drag a translucent highlighter across a PDF. The words underneath stay selectable and searchable, exactly like a real marker pen.
- Runs in your browser
- Files are never uploaded
- Free, no account
Drag across a passage to lay a translucent highlight over it. The words underneath stay readable, selectable and searchable. Everything happens in this browser tab — you can turn off your network connection first and it will still work.
Highlighting that behaves like a real marker
Most tools draw a semi-transparent rectangle over your text. The result is a washed-out grey block: the highlight lightens the black letters as much as it tints the white paper, and the passage becomes harder to read than it was before.
A marker pen does not work that way. Ink filters light rather than adding it, so it darkens the paper and leaves already-black text black. That is multiply blending, and it is what this tool writes into the PDF. Yellow over white paper gives yellow; yellow over black type gives black. The passage stays crisp, and the highlight looks like a highlight.
Choosing a colour
| Colour | On screen | Photocopied or printed mono | Best for |
|---|---|---|---|
| Yellow | Bright, unmistakable | Very light grey — text stays fully legible | Everything, unless you need a second colour |
| Green | Calm, reads as "approved" | Mid grey | A second category on a screen-only document |
| Blue | Cool, low contrast with blue links | Dark grey — can obscure small type | Screen reading only |
| Red | Alarming, hard to read over | Dark grey | Short flags, not passages |
Around 40% opacity is the sweet spot. Lower and it disappears when the page is printed; higher and even multiply blending starts to fight with the type.
Highlighting line by line
Drag one rectangle per line of text. It takes a few seconds longer than dragging one big block, and it is what makes a highlight look right: the last line of a paragraph is usually short, and a full-width block over it highlights a lot of empty paper.
Aim to cover from just below the baseline to just above the ascenders. Overshooting into the line above is the most common mistake and the most visible one — zoom in to 150% or 200% and the alignment becomes easy.
Your text stays searchable
Because the highlight is a coloured rectangle rather than a re-rendered page, the text underneath is completely untouched. Ctrl+F still finds it, a screen reader still reads it, PDF to Text still extracts it, and the file size barely moves — a highlight is a handful of bytes.
That is the opposite of what happens with tools that flatten the page to an image in order to "burn in" the highlight, which destroys the text layer for the sake of a coloured rectangle.
Studying from a highlighted PDF
For revision, highlight sparingly — highlighting half a page marks nothing. A useful discipline is one highlight per paragraph maximum, plus a margin note in the Text tool summarising why it mattered. When you come back to the document, the notes are what you read; the highlights just tell your eye where to look.
If you want the marked-up copy printed, check it in grayscale first with PDF to Grayscale. That shows exactly how each colour will land on a mono printer before you spend the paper.
Questions
Why is my text still readable under the highlight?
Because the highlight is drawn in multiply blend mode, the same way ink behaves on paper: it darkens what is beneath it instead of covering it. A plain translucent rectangle would wash the text out to grey; multiply keeps black text black and turns white paper yellow. That is why highlights made here look like a real marker rather than a tinted pane of glass.
Which colours work best?
Yellow is the default because it survives black-and-white printing as a light grey without obscuring anything. Green and blue read well on screen but print as heavy grey. If the document will be photocopied, pick yellow and keep opacity around 40%.
Can I highlight several lines at once?
Drag one rectangle per line — that is how highlights look right when the last line of a paragraph is short. For a whole block, one tall rectangle across the full column also works and is quicker; the trade is a rectangular edge instead of a ragged one.
Will the highlights show up in other PDF readers?
Yes, in all of them. They are page content rather than annotation objects, so there is no reader setting that hides them, no comment pane to enable, and no risk of them disappearing when the file is printed or converted.