How to Annotate a PDF on Mobile
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Annotating a PDF is how you turn a document from something you read into something you respond to — highlighting the clause that matters, leaving a comment for a colleague, circling the figure that's wrong. On a phone or tablet, with a finger or a stylus, it's often more natural than at a desk, because you're marking the page the way you'd mark paper.
This guide covers the annotation tools worth knowing on mobile using the PDF Editor app: highlights, comments, freehand drawing, and shapes. It runs on iPhone and Android, works offline, and keeps the document on your device.
The aim isn't to cover the page in ink — it's to leave markup that the next person (often future you) can actually read and act on.
Step by step
- 1
Open the PDF in the PDF Editor app
Import the document from Files, Mail, Drive, or any share sheet. Annotation tools sit in the editing toolbar.
- 2
Highlight the key passages
Select the highlighter, pick a colour, and drag across the text you want to mark. Use colour deliberately — one colour per type of note reads far better than a rainbow.
- 3
Add comments for context
Drop a sticky comment where a highlight needs explanation. Comments keep your reasoning attached to the spot without cluttering the page itself.
- 4
Draw and circle freehand
Use the pen tool to circle a figure, underline a line, or sketch a correction. A stylus gives cleaner strokes than a fingertip if you have one.
- 5
Add shapes or arrows where they help
An arrow pointing at the problem or a box around a section communicates faster than words. Use them sparingly so they stand out.
- 6
Save and share the marked-up copy
Export a copy with your annotations and share it back. Keep the clean original if you'll need an unmarked version later.
Tips
- Assign meaning to colours — say, yellow for questions, green for approvals — and your markup becomes scannable instead of decorative.
- A stylus (Apple Pencil or S Pen) transforms freehand annotation. If you have one, palm rejection and pressure make it feel like marking paper.
- Comments beat cramming notes into the margin. They expand when tapped and keep the page legible.
- Don't over-annotate. A page buried in ink is as useless as one with no marks — highlight what matters, not everything.
- Keep an unmarked original. Annotations are great for review, but the next reviewer may want a clean copy to mark themselves.
Try it on your phone
Annotating is where a phone or tablet genuinely beats a desk: you mark the page directly, the way you would on paper. The PDF Editor app supports highlights, comments, drawing and shapes with stylus support, all offline and on-device — your markup never leaves your hands.
