How to Annotate a PDF Online for Free

By the CustomizedPDF Team · How-To · 5 min read

How to annotate a PDF (step by step)

1. Open the CustomizedPDF Annotate tool.
2. Add your PDF — it opens instantly from your device, with no upload.
3. Use the tools to highlight text, add comments or text boxes, draw freehand, or add shapes and arrows.
4. Position your annotations, then download the marked-up PDF.

What can you annotate?

• Highlight key passages in a contract, study guide, or report.
• Comment with sticky notes or text boxes for feedback and review.
• Draw & shapes — circle important figures, add arrows, or sketch corrections.
• Need to add a signature instead? Use the Sign PDF tool. Editing the actual text? Use Edit PDF.

Is it private to annotate confidential PDFs online?

Yes — annotation happens in your browser, so the document never leaves your device. That matters for reviewing contracts, medical forms, or student records. Learn how we keep your files local.

Annotate your PDF now

Open the free Annotate PDF tool →

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Annotating vs Editing vs Redacting

These three get conflated constantly, and the difference matters a great deal when the document is confidential.

• Annotating adds comments and marks on top of the page. The original content stays exactly as it was, visible underneath.
• Editing also draws a new layer, but with shapes and text intended to alter how the page reads — whiting out an error, typing a correction.
• Redacting permanently deletes the underlying content. It is the only one of the three that actually removes anything.

If your goal is to hide a figure before sharing, annotation is the wrong tool — a highlight or a filled box sits over the text, and the text is still selectable underneath.

Annotations That Survive the Round Trip

The practical question with any annotation is whether the other person will see it. Marks drawn into the page itself — highlights, boxes, arrows, text you place — are part of the page and display identically in every reader, on every device, and in print.

Reader-specific comment objects behave differently. Sticky notes and threaded comments created in one application do not always render in another, and frequently disappear when the file is printed or flattened. If your markup absolutely must reach the recipient, drawn annotations are the safer choice.

Making Review Markup Actually Useful

• Say what you want, not just where. “Confirm this figure with finance” is actionable; a lone highlight is a puzzle.
• Use colour consistently. One colour for questions, another for required changes. Tell the recipient the scheme in your covering message.
• Highlight sparingly. A page that is mostly yellow communicates nothing.
• Number your points on long documents so they can be discussed by reference on a call.

Annotating Scanned Documents

If the page is a scan, there is no text underneath — only an image. You can still draw on it, but you cannot select or highlight words, because there are no words as far as the file is concerned. Run OCR first to create a text layer if you need to highlight passages rather than draw over them.

Before You Send It Back

Annotated drafts often circulate widely. Two things worth doing first: strip the metadata, which carries your name and software into every copy, and check that nothing you meant to obscure is merely covered rather than redacted. If the file has grown large with added graphics, compress it before emailing.

Frequently asked questions