How to sign a PDF from an email on iPhone (and send it back)

The most common signing moment there is: an email lands with a PDF attached — a lease, a school form, a contract — and one line at the bottom is waiting for your signature. The sender doesn’t care how you sign it. They just want it back, today, without you finding a printer.

Here are your two real options on an iPhone, honestly compared.

Option 1: iOS Markup (free, built in)

Apple’s built-in Markup can sign an attachment without installing anything:

Open the email in Mail and tap the PDF attachment.
Tap the pencil (Markup) icon in the top corner.
Tap + → Signature — draw one with your finger, or pick one you’ve saved before.
Drag it over the signature line, resize with the handles, tap Done.
Mail offers to attach the signed copy to a reply — send it.

Where Markup is enough: one-off signatures on simple documents. It’s free and already on your phone — if this covers you, you don’t need an app.

Where it gets annoying, honestly: the signature is a raw finger-drawing (redrawing a decent one on glass takes a few tries); dates and initials are manual text boxes you fiddle into place; multi-page documents that need initials on every page become real work; and Gmail/Outlook users have to detour through Files to reach Markup at all.

Option 2: a signature app (the repeat-signer’s route)

If signing happens more than occasionally — or you want it to look like your signature rather than a shaky glass-drawing — a dedicated app changes the economics of the whole thing:

Open the attachment in Mail, Gmail or Outlook and tap Share.
Choose Signed (or save to Files and import from there).
Your saved signature, initials and an auto-filled date are one tap each — drop them where they belong. In Signed you create your signature once: draw it properly, type your name in a real handwriting style, or let AI generate one.
Tap Finish — you get a clean, flattened PDF — and share it straight back into a reply.

After the one-time setup, the whole round trip is genuinely under a minute, and the result is identical on every document you’ll ever sign.

The privacy angle worth knowing: the classic e-sign services (the upload-your-document-to-our-cloud kind) are built for businesses sending contracts out. For receiving and returning documents, you don’t need any of that — Signed is local-first: the PDF never leaves your phone.

Which should you pick?

You sign something twice a year → Markup. Free, fine, done.
You sign monthly or more, or care how it looks → an app pays for itself in avoided fiddling the first week.
The document is high-stakes legal work → whatever tool you use, a signature image on a PDF may not be the whole requirement — check what’s actually needed for that document type.