How to add an electronic signature in Proton Mail on iPhone
What you actually have is an encrypted-in-transit attachment on a message in Proton Mail. Here is how it gets signed and sent back, on the phone in your hand — no printer, no scanner, no account.
Option A · free · nothing to install
Apple Markup — free, already on your iPhone
Markup runs entirely on the phone, so the decrypted file never goes anywhere. Markup ships with iOS at no cost, holds one saved signature, and can send the marked-up copy straight back from the same screen.
- Open what you have in Proton Mail. What you are dealing with is an encrypted-in-transit attachment on a message in Proton Mail.
- Get it to a screen that can sign. Tap the attachment to decrypt and preview it, then use the share icon to send it to Markup or a signing app.
- Sign it. Tap the + at the bottom right of Markup, choose Signature, sign with your fingertip, tap Done, then drag the signature onto the line and pull the blue handles until it sits on the line rather than through the text underneath.
- Send it back. Compose the reply in Proton Mail and attach the signed copy so it goes back with the same protection.
If this is a one-off, stop here. The free route above signs the document and sends it back. Where it gets slow is repetition: Apple Markup holds one signature and no initials, text boxes do not snap to the form’s lines, there is no date shortcut, and nothing you place is flattened into the page.
Option B · with Signed
Sign it with Signed instead
Same document, fewer taps — because the signature, the initials and the date are already saved, and everything you place is flattened into the exported PDF.
- Share the PDF into Signed. From the same share sheet you reached out of Proton Mail, pick Signed — or import the PDF from inside the app. It stays on your iPhone: nothing is uploaded and there is no cloud copy.
- Drop in the signature you already saved. Tap the signature line and place the signature you made once — drawn with a fingertip, typed in a real handwriting style, or generated with AI. You never redraw it per document.
- Fill in the rest of the page. Add the date, your initials, your name, text and checkmarks with the matching tools. Today’s date fills itself in and saved initials are one tap per page.
- Export a flattened PDF and send that. Export the signed copy flattened, so the signature and every field become part of the page rather than a layer someone can drag off it. Then compose the reply in Proton Mail and attach the signed copy so it goes back with the same protection.
The catch with Proton Mail
Once you share the attachment out of Proton Mail it is an ordinary file on your phone. If the point of using Proton is that the document never sits in someone else’s cloud, sign it with something that works on-device rather than uploading it to a web service.
Signed signs PDFs. It does not convert file formats, sync your files, or send documents out for someone else’s signature — which is why anything that is not already a PDF goes through Proton Mail’s own export first.
Other email apps
Signing from a different app
See all 62 apps → · know the document but not the app? Pick it by document type → · comparing services instead? See the e-sign alternatives →
Signed is a signing tool, not legal advice. Whether an electronically signed copy is accepted depends on the document, the counterparty and where you are — for anything high-stakes, check what your jurisdiction requires, including whether a notary or witnesses are needed. Proton Mail is a trademark of its respective owner and this page is not endorsed by or affiliated with it; Apple, Markup, iPhone and iOS are trademarks of Apple Inc. App interfaces change, so a menu may have moved since this was written.