How to write on a PDF on iPhone with your finger

You have a PDF open on your phone and you want to write on it by hand. Circle a paragraph. Scrawl “yes, approved” in the margin. Fill a blank line in your own handwriting instead of a typed font. Put your name at the bottom.

Your iPhone does all of this for free, with your fingertip, no app and no account. The tool is called Markup, it has shipped with iOS since 2017, and it’s hidden behind an icon that looks like a pen tip. Here’s how to use it properly — and, honestly, the one job it’s bad at.

Write on a PDF with your finger (free, built in)

Open the PDF. In Files, Mail (tap the attachment), Messages, or almost any app that previews PDFs.
Tap the Markup icon — the pen-tip circle in the top-right corner. On some screens it’s behind the ⋯ menu → Markup.
Pick a tool from the bar at the bottom:
- Pen — a firm, even line. Best for writing words.
- Marker — a chisel-tip highlighter. Best for highlighting a line of existing text.
- Pencil — a textured, softer line. Good for rough circles and ticks.
- Eraser — tap it twice to choose Pixel Eraser (rubs out part of a stroke) or Object Eraser (removes a whole stroke in one tap).
Tap the tool a second time to open its size and opacity sliders, and tap a colour dot to change ink colour. Black or blue reads best on a document.
Write on the page with your finger. Pinch to zoom in first — this is the single biggest improvement most people never make. Zoomed in to about 200%, your finger covers a much smaller share of the line and your handwriting stops looking like a toddler’s.
Tap Done, then Save File To… or share it. The handwriting is now baked into the PDF for whoever opens it next.

That’s the whole free answer. If you’re annotating a document once, stop reading here — you don’t need an app for this.

The three tricks that make finger-writing legible

Zoom in hard before you write. Everyone writes badly at 100%. At 200–300% the same finger produces normal-looking handwriting.
Rest your palm off the glass. iPhone Markup has no palm rejection worth trusting on a phone-sized screen — a resting palm will draw a stray line. Hold the phone in one hand and write with the other.
Undo is two fingers. Double-tap with two fingers, or use the arrow at the top. Faster than switching to the eraser for a stroke you just botched.

Drag the little handle on the toolbar and it collapses into a small circle at the edge of the screen. Tap the circle to bring it back. Nothing is broken — it’s a deliberate gesture that people trigger by accident constantly.

What Markup can’t do: fill in fields

Markup draws on top of the page. It doesn’t understand the page. That means:

What you want	Markup with your finger	Reality
Circle, tick, scribble a note	✅ Perfect	This is exactly what it’s for
Highlight a sentence	✅ Marker tool	Works well
Handwrite a word on a blank line	✅ Fine once you zoom	Slightly wobbly, but fine
Type into a real PDF form field	❌	Different job — see add text to a PDF on iPhone
Put the same signature on document after document	⚠️ Painful	Read on

The honest weak spot: anything you write more than once

Finger-drawing is great for one-off marks. It’s genuinely bad at repetition, because Markup keeps nothing. Every document starts from an empty page: draw the signature again, draw the initials again, write today’s date again — and none of them will look like the last one you drew.

For a scribbled “approved” in a margin, that doesn’t matter. For a signature it does, because the whole point of a signature is that it looks the same every time.

Markup has a partial answer here: + → Signature stores a signature separately from the drawing tools, and that one is reusable. It’s worth setting up if signatures are all you need. But it’s one signature, with no initials, no date stamp, and no way to keep a business one and a personal one apart.

When an app earns its place

If the same marks go on documents week after week, a dedicated app changes the arithmetic. In Signed you create your signature once — draw it with your finger (zoomed to a full-screen canvas, which is far easier than a phone-sized PDF), type your name in a real handwriting style, or let AI generate one from your name — and it’s saved. After that, your signature, your initials, an auto-filled date, text and checkmarks are one tap each on any PDF you import, and the export is a clean flattened file.

Two things worth knowing before you decide:

It’s local-first. The classic e-sign services upload your paperwork to their cloud. Signed doesn’t upload documents — the PDF stays on your phone.
It’s not a legal service. A signature you place on a PDF is a signing tool doing its job, not legal advice. If a document is high-stakes, check what that document type actually requires before you rely on any app, ours included.

Finger vs Apple Pencil

If you have an iPad and a Pencil, use them — the pressure sensitivity and palm rejection make handwriting on a document genuinely pleasant instead of merely acceptable, and the steps are slightly different. That’s covered in signing a PDF on iPad with Apple Pencil.

On an iPhone with no stylus, the zoom trick above closes most of the gap. A cheap capacitive stylus closes a bit more, but it’s not required — a fingertip at 250% zoom is fine.

So, which route?

Annotating a document today → Markup, free, done in a minute.
The same handwriting on documents every week → save the signature somewhere reusable, whether that’s Markup’s signature slot or an app.
You just want a good-looking signature to start with → build one first in the free signature generator, then use it wherever you like.