Highlight PDF

Runs in browser PDF Editing & Annotation

Drag across the words and the highlight snaps to the text lines, exactly like a desktop reader. Choose the colour and opacity; switch to underline or strikethrough in the same toolbar. Highlights are saved as standard annotations (or flattened into the page if you prefer).

Privacy: Processed locally in your browser. Your file is not uploaded.

What is a PDF annotation, and why does whiting-out text not remove it?

An annotation is an object attached to a page on top of its content: highlights, underlines, strike-throughs, sticky notes, free text, ink drawings, shapes, stamps and signature fields are all annotation types defined in ISO 32000, stored in the page's /Annots array and editable or removable later. Flattening draws them permanently into the page content. The PDF editor on this site keeps only highlights, underlines, strike-throughs (unless you choose to flatten them) and sticky notes as annotations; the text, drawings, shapes, stamps and signature images it adds are written straight into the page content and are permanent. A white rectangle drawn over text is exactly that — a shape on top — so the text beneath still exists, copies and searches; only redaction, which deletes the underlying content, removes it.

Security note: Covering text with a shape is not redaction: the hidden text remains in the file and can be selected, extracted or found by search. Use a redaction tool that removes content, then check the result by searching for the removed text.

Read the guide: How to Edit a PDF Without Uploading It

How to use Highlight PDF

  1. Drop a PDF.
  2. Drag across the words to highlight.
  3. Change the colour if you like; add more.
  4. Click "Save PDF" and download.

Highlight PDF features

  • Snaps to words and lines using the text layer
  • Any colour and opacity
  • Underline and strikethrough on the same toolbar
  • Saved as standard annotations or flattened
  • Rectangle fallback on scanned pages
  • Local processing

Highlight PDF example

Mark the key figures in a report

Input:

Drag over three numbers on page 5; yellow, 45 %

Output:

report-highlighted.pdf — three Highlight annotations with QuadPoints, multiply blend

Frequently asked questions about Highlight PDF

Why does the highlight snap to the text?

The tool reads the text positions from the page and builds the highlight from the words under your selection, one strip per line, so it looks like a highlighter and not like a box. On a scanned page with no text layer it falls back to the exact rectangle you drew.

Can other people remove the highlight?

By default it is a standard Highlight annotation, so any PDF reader can show, move or delete it — which is usually what reviewers want. Choose "Flatten into the page" when saving if the highlight must be permanent.

Does it work on scanned PDFs?

Yes, as a rectangle: a scan has no text to snap to. Run OCR PDF first if you want the highlight to follow the words.

Is my PDF uploaded to a server?

No. The file is opened and processed by your browser with WebAssembly and JavaScript; nothing is sent to Mutqan Soft or anyone else. Close the tab and the file is gone. Downloading the result needs a free account — no subscription, no payment.

Can I use it on a password-protected PDF?

Yes, if you know the password: the file list asks for it once and every operation then works on the decrypted pages. The output is saved without a password unless you protect it again.

Technical notes

The page’s text runs (positions from pdf.js getTextContent) that meet the dragged rectangle are clipped to it and merged per line into QuadPoints. The annotation carries an appearance stream (a form XObject filling each quad with /BM /Multiply), so readers that ignore QuadPoints still show it correctly; "flatten" draws the same rectangles into the page with a Multiply blend mode instead.

References