How to Highlight and Annotate a PDF Online

Highlighting and annotating a PDF used to mean printing it, grabbing a marker, then scanning it back in. Online, it takes seconds. With a free online PDF editor you can highlight key lines, underline clauses and leave notes directly on the page — on a laptop or a phone, with nothing to install.

Highlighting vs. annotating — what's the difference?

Highlighting draws attention to text that's already there: the important sentence, the deadline, the figure that matters. Annotating adds something new on top — a note, an arrow, a shape or a comment that explains or flags part of the document. Most markups use a mix of both.

How to highlight a PDF online

• Open your file in the free editor — no sign up required.
• Pick the highlight tool and choose a colour.
• Drag across the text you want to emphasise.
• Switch to underline for lines that need a lighter touch.

How to annotate a PDF online

• Add text notes anywhere on the page to explain or summarise.
• Draw or sketch freehand to circle and connect ideas.
• Drop in shapes and arrows to point readers straight to what matters.

Great for everyday documents

• Marking up study notes and lecture handouts.
• Reviewing contracts and flagging clauses for discussion.
• Giving feedback on reports, designs and proposals.
• Filling in and signing-off forms on the go.

Do it on any device

Because everything runs in your browser, the same tools work on desktop, tablet and mobile. There's no app to download and no account to create — open the editor and start marking up. New to it? See the guide to editing a PDF for free first.