How to sign a PDF offline on iPhone (no internet needed)

You’re on a plane, in a basement, on a train through a tunnel, or just out of data for the month — and the PDF that needs signing is sitting on your phone. The good news is the part everyone worries about is the part that was never online to begin with: placing a signature on a PDF is a local operation. Your iPhone draws the mark, writes it into the file, and saves it. No connection is involved.

What actually needs a connection is only the two ends of the journey — getting the document onto the phone, and sending the signed copy back. Plan for those and the middle takes care of itself.

First: make sure the file is really on your phone

This is the step that catches people out. A PDF you can see in Mail or Files isn’t always downloaded — sometimes you’re looking at a placeholder that fetches on demand.

In Mail: open the attachment once while you still have signal. Once it has rendered, it’s cached on the device.
In Files (iCloud Drive): long-press the file → Download Now (or check it doesn’t have the little cloud-with-arrow badge). Better still, drag a copy into On My iPhone, which is never a placeholder.
From a chat app: tap the attachment to download it, then Share → Save to Files so it survives the app clearing its cache.

Do this before you take off, not after.

Option 1: iOS Markup — completely free, completely offline

Apple’s built-in Markup does not phone home. It works in Airplane Mode exactly as it works on Wi-Fi:

Open Files (or the Mail attachment) and tap the PDF.
Tap the Markup icon (the pen tip) in the top corner.
Tap + → Add Signature → draw with your finger → Done.
Drag it onto the signature line, resize with the handles.
Tap Done — the change is written to the file on the device.

Need to type a date or a name too? The same + menu adds a text box, and the pen, marker and pencil tools all work offline as well — that’s the same toolkit covered in writing on a PDF on iPhone with your finger.

And you can send it before you have signal. In Mail, sign the attachment, tap Reply, attach the signed copy and hit send — the message drops into the Outbox and goes out by itself the moment a connection returns. You genuinely can finish the whole job mid-flight.

If that covers you, you’re done — you don’t need an app. Markup is free, already installed, and offline by nature.

Where the free route starts to grate

Markup’s limitation offline is the same as its limitation online, just more annoying when you’re bored on a plane with three documents to get through:

It doesn’t reliably keep your signature. More often than not you’re redrawing it with a fingertip on glass, and the fourth attempt never quite matches the first.
Dates and initials are manual. Each one is a text box you position and size by hand.
Multi-page documents are a slog. Initialling every page one text box at a time is exactly the kind of repetition a phone should be doing for you — see adding initials to every page of a PDF.

Option 2: a signature app — and why “offline mode” is the wrong question

People often search for an offline signing app expecting to find a setting to toggle. In Signed there isn’t one, because there’s nothing to toggle: the app is local-first by architecture. Documents, signatures and initials are stored on the iPhone, there is no Signed cloud, and nothing is uploaded at any point. Offline isn’t a mode — it’s just how the app already works. (The privacy consequences of that are a separate story: does Signed upload my documents? and is it safe to sign documents online?.)

In practice, with the radio off:

Import the PDF from Files, Mail or a share sheet.
Tap your saved signature — created once, in your own hand, typed in a handwriting style, or generated for you — and drop it where it belongs.
Initials and today’s date are one tap each, on as many pages as the document has.
Export a flattened signed PDF back to Files, or straight into a queued Mail reply.

The one honest catch: do the setup while you still have a connection. Downloading the app from the App Store and creating your signature the first time is best done on the ground. After that, the signing itself never needs the network again.

What genuinely does break offline

Worth knowing so you’re not stuck waiting on a spinner:

Cloud e-signature services (the send-an-envelope-for-countersignature kind) do the signing on their servers. No connection, no signature — the web page simply won’t load. If your document arrived as a “click here to sign” link rather than an attached PDF, that link needs internet, full stop.
Our own free signature generator runs in a browser, so it needs a connection too. Use it to create a signature before you travel, save the PNG, and it’s yours offline afterwards.
Anything that syncs — iCloud Drive uploads, shared folders, Google Drive — will queue rather than fail, but the other side won’t see the file until you’re back online.

The short version

Get the file onto the device before you lose signal. This is the whole trick.
Markup signs it offline for free. For an occasional signature, stop here.
A local-first app signs it offline too, with the signature, initials and date you set up once already waiting — worth it if signing is a routine rather than an event, and the same reasoning as signing a PDF without printing.
Send from the Outbox, and it leaves the moment you land.