How to sign a document sent on WhatsApp on iPhone

Freelance invoices, rental agreements, cross-border contracts, the form your accountant needs back by tonight — a lot of paperwork never touches email any more. It arrives as a PDF in a WhatsApp chat, and the person who sent it is already typing “can you sign and send back?”.

The first thing worth knowing is why this feels harder than signing an email attachment: WhatsApp opens PDFs in its own built-in viewer, and that viewer has no markup or annotation tools. There’s no pencil icon to tap. Nothing is broken — you just can’t sign inside WhatsApp, so every route below starts by getting the file out of the chat.

Step 1: get the PDF out of the chat

This step is the same no matter how you sign afterwards.

Tap the document in the chat to download and open it.
Tap the share icon in the viewer (or press and hold the document bubble in the chat and choose to share/forward it).
In the iOS share sheet, either Save to Files — Downloads or iCloud Drive, anywhere you’ll find it again — or send it straight into the app you’ll sign with.

That’s it. Once the PDF is in Files, it’s an ordinary iPhone document and everything below is the same as signing a PDF that arrived by email.

Step 2, option A: iOS Markup (free, already on your phone)

If you only need this once, don’t install anything:

Open the Files app and tap the PDF you just saved.
Tap the pencil (Markup) icon in the top corner.
Tap + → Signature — draw one with your finger, or reuse one you’ve saved before.
Drag it onto the signature line, resize it with the corner handles, tap Done.
Tap Share → WhatsApp → pick the chat → send.

Where this is genuinely enough: a single signature, on a document nobody is going to scrutinise, that you’ll never have to sign again. It’s free and it works.

Where it starts to cost you time, honestly: the signature is a raw finger-drawing, so it takes a few tries to get one you’re happy to put on a contract; dates and initials are manual text boxes you nudge into place; and Markup adds your signature as an annotation layer rather than baking it into the page — which is why a signature can occasionally shift, or fail to appear the same way, once the file passes through someone else’s viewer or printer. If that matters here, it’s worth flattening the signed PDF before you send it back.

Step 2, option B: a signing app (if this keeps happening)

If documents arriving by chat is a regular part of your work rather than a one-off, the maths changes — the setup cost is paid once and every document after that is a few taps:

In the WhatsApp viewer, tap Share and choose Signed (or save to Files first and import from there — either works, since Signed receives files through the standard iOS share sheet like any other app).
Your saved signature, initials, date, name, text and checkmarks are one tap each — drop them exactly where they belong on the page.
Tap Finish to export a clean, flattened PDF.
Share it back into the WhatsApp chat from the export screen.

You create the signature once — draw it properly, type your name in a real handwriting style, or let AI generate one from your name — and it looks identical on every document from then on. If you’d like to see what your name looks like as a signature before installing anything, the free signature generator does that in the browser.

One honest clarification: there is no WhatsApp integration here, and no app can add one. WhatsApp doesn’t let other apps edit files inside the chat. The share sheet is the connection — file out, sign, file back in.

The privacy part, since it’s a chat

Paperwork that arrives in a private chat often shouldn’t be uploaded anywhere. Most classic e-sign services are built around exactly that: your document goes to their cloud, gets processed there, and comes back. For simply receiving and returning a signed document, you don’t need any of that — Signed is local-first, so the PDF stays on your phone the whole time and the only copy that leaves is the one you send back to the chat yourself.

A few things people run into

The document is a photo, not a PDF. Someone photographed a printed page and sent the image. Save it to Photos, then treat it as a scan — signing a scanned document on iPhone covers that path.
The file is greyed out or won’t open. Usually it hasn’t finished downloading — tap it once in the chat and wait for the download arrow to clear.
They asked for initials on every page too. That’s a separate job from one signature; adding initials to every page walks through it.
Whether a signature sent over chat is enough for the document at hand is not a formatting question, and it isn’t one a signing app can answer. If the paperwork is high-stakes, check what’s actually required for that document type — and if real money or a legal obligation rides on it, ask the counterparty or a professional what they need. Signed is a signing tool, not legal advice.