How to highlight text in a PDF

Highlighting a PDF, step by step

1. Open the Highlight PDF tool.
2. Select or drag in your PDF, and a preview of page 1 renders right in your browser.
3. Drag across any passage to lay a highlight over it; use Prev/Next to move through the document and keep marking as you go.
4. Pick a color before you drag (yellow, green, pink or blue) and switch colors to code different kinds of note.
5. Press Add highlights and download the marked-up PDF.

Real highlights, not fragile annotations

Most PDF readers offer highlight annotations: marks that live in a separate layer, are editable by anyone who opens the file, are sometimes silently stripped when the PDF passes through other software, and frequently vanish when the page is printed. This tool works differently. It draws each highlight into the page content itself as a translucent colored rectangle using a multiply blend at reduced opacity, the same optical trick as a real highlighter pen, where the ink darkens the paper but the words show through. Because the color is baked into the page, it travels everywhere the file goes and prints exactly as you see it.

Why a multiply blend keeps text readable

The multiply blend is the reason the words underneath survive. Instead of painting an opaque block on top of the text, it multiplies the highlight color with whatever is beneath it, so dark text stays dark and only the white paper turns yellow, green, pink or blue. The practical result is that your highlighted sentence reads just as easily as before, the opposite of what happens when someone drops a solid colored box over a line and hides it.

The text underneath stays alive

Crucially, the highlight is only a visual overlay; it never touches the text layer. That means the words you marked remain selectable, searchable and copyable, and you can still pull the passage out later with PDF to Text, quotes and all. A highlighted study or contract is therefore just as machine-readable as the original: you have added emphasis without sacrificing any of the function.

Where highlighting earns its place

This is the tool for close reading. Reviewing a contract: flag every clause you need to renegotiate so nothing is lost between reads. Studying a paper or report: mark the findings and figures you will cite, then come back to only the colored lines. Coordinating a team: circulate one PDF with the key passages highlighted so everyone is looking at the same sentences instead of describing them over email. For marks that go beyond a colored band, such as arrows, circles or crossings-out, reach for Draw on PDF, and for typed notes use Add Text.

Nothing leaves your browser

Every stage, from rendering the page preview to laying down the highlights to writing the final file, happens locally in your browser, so a confidential contract or an unpublished manuscript is read and marked up without ever being sent anywhere. For sensitive documents that is the whole appeal, and the underlying reason it works is explained in are online PDF tools safe.

Frequently asked questions

Can I remove a highlight later? Before you download, Undo last removes the most recent one and Clear this page clears the current page. After downloading it is part of the page, so rerun the tool on your original.

Is the highlighted text still selectable? Yes. The highlight sits over the text as a transparent layer; the text itself is untouched and stays searchable and copyable.

Does the highlight print? Yes. It is drawn into the page content, so it appears on paper and in every reader, unlike annotation-layer highlights that often print blank.

Can I highlight across many pages? Yes. Move through with Prev/Next and mark whatever you need; each highlight is kept per page and written in on download.

Will other people see my highlights? Yes, and they cannot toggle them off, because the color is baked into the page rather than stored as an optional annotation.