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Annotate PDF

Add highlights, text, shapes, and drawings to your PDF

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This tool lets you select text to add a colored highlight, drop a sticky note anywhere on a page, or draw freehand with a pen tool, all inside the browser with nothing uploaded. Highlights use the PDF's embedded text layer to snap to actual words and lines; notes and drawings are placed at whatever page coordinates you click or drag. The detail that catches people out: on a scanned or image-only PDF there is no text layer to snap to, so a highlight there is really just a translucent box wherever you dragged, not a marking tied to specific words.

How it works

Text-aware highlighting
When the page has an embedded text layer, dragging over text selects whole words and lines the same way copy-paste selection would, and the highlight rectangle is generated from that selection's bounding boxes. Without a text layer - common on scanned pages - the tool has no words to detect, so highlighting falls back to a plain draggable rectangle with no relation to underlying content.
Notes and drawings as separate annotation objects
Sticky notes and freehand ink marks are written as standard PDF annotation objects anchored to page coordinates, kept apart from the original content stream. That keeps the source text and images untouched and lets each annotation be moved, edited, or deleted on its own, but it also means the marks live in a layer that some viewers, print settings, or text-extraction tools can choose to hide or ignore.

When to use it

  • Highlighting the clauses under negotiation in a contract draft and attaching a note to each one before sending it back for review.
  • Marking up a scanned lecture handout or journal article by circling figures and underlining passages, since there's no selectable text to highlight through.
  • Color-coding a shared report by topic or reviewer with highlights, then adding quick freehand arrows or circles to flag specific numbers before a meeting.

Worth knowing

  • On scanned or image-only PDFs there's no text layer, so highlights can't snap to words - they become a plain rectangle that may not align neatly with the text underneath.
  • Sticky notes typically collapse to a small icon on the page; the comment text stays hidden until someone clicks to expand it, so a quick visual scan of the page can miss them entirely.
  • Because annotations sit in a layer separate from the page content, some viewers, print dialogs, or text-extraction tools may not display or include highlights, notes, or drawings unless the file is flattened or the viewer is set to show comments.

Frequently asked

Can I still select and copy text underneath a highlight I added?
Yes in most viewers - the highlight is a translucent annotation layered on top of the text, not an edit to the text itself, so selecting and copying the underlying words still works normally. The one exception is a viewer that flattens annotations into the page on export, which can occasionally interfere with text selection afterward.
Will someone opening this PDF in a different app see my highlights and notes?
In most current PDF viewers, yes, since highlights, notes, and ink drawings are standard PDF annotation types. Some simplified mobile readers or older software may hide annotations by default, or may not render freehand ink marks at all, so it's worth checking in the recipient's actual viewer if it matters.

References

All PDFb2 tools