Sign a PDF on iPhone and Android: three ways

Most documents people are asked to sign arrive on a phone, often in the evening, often with a deadline of tomorrow. Signing on the phone is easy. Knowing which kind of signing you have just done is the part worth a minute, because a signature drawn onto a PDF and a signature given through a signing link look almost identical on the page and are very different as evidence.

Way one: the phone’s own tools

On an iPhone, no extra app is needed. Apple’s iPhone guide describes filling out forms and signing documents you receive: tap a field to type into it, then to add a signature tap the add button, choose Add Signature, sign your name with your finger, tap Done and drag the signature into place. The same guide notes that the iPhone saves a signature for next time and that you can keep more than one, such as a nickname or your initials, and Apple’s Markup article shows the tool working on a PDF attached to an email in Mail. The Preview app on iPhone can also open a PDF form, fill its fields and add a signature.

Before sending the signed copy back, open it again and check two things. The signature sits on the right line of the right page, and every field you typed into kept its value. Markup lets you drag and resize a signature freely, which is convenient and also how a signature ends up half over a clause. Then send the file itself rather than a screenshot of it, so the recipient gets the whole document and not one page.

Android has no single equivalent, because different manufacturers ship different PDF viewers. Most people install a PDF app that supports signing and draw with a finger in much the same way.

What both leave behind is the same: an image of your signature placed on a page, saved into a new copy of the file. Nothing in the file says who drew it, when, or whether the text around it changed afterwards. That is fine for a permission note to a sports club. It is thin for an employment contract.

Way two: a PDF app

A dedicated PDF app adds convenience, such as stored signatures, typed field values and sharing straight back to the sender. Some also offer their own request and signing services with more records attached. Google’s eSignature feature in Docs and Drive, for example, lets a sender request signatures on a PDF and adds an audit trail page to the final file once everyone has signed.

The question to ask of any app is simple: does the finished file carry anything beyond the picture? If the answer is no, you have done the same thing as way one with nicer buttons.

Way three: a signing link

A signing link is sent by the person who needs the signature. You open it in the phone’s browser, prove who you are if they asked for a check, accept a consent statement and sign. There is no app to install.

On a phone this looks different by design. Below 560 pixels wide the signing page switches to a compact mode: the document becomes read only and every field you need to type into moves to a Complete your details panel above it. The embedded permission slip signing example was signed on a screen 390 pixels wide. The parent, Naomi Tran, typed an emergency contact and phone number into the panel, added a note about a mild peanut allergy and the EpiPen in her son’s bag, marked the consent box and drew her signature with a finger on a pad that opens full width. The school got a certified PDF back, and so did she.

Documents with several signature spots do not mean several drawings. One drawn signature fills every signature, initials and signature block spot assigned to you, and a header button reading Signature 1 of 3, and so on, scrolls to each spot in turn. On the employment contract signing example, one drawing filled two initials spots and a signature.

If the sender is standing in front of you, they can hand you their own device instead. The liability waiver signing example shows a climbing centre handing a tablet to a visitor at the front desk, with the in person start recorded before the signature.

Drawn or typed, and what the file carries

On a signing link, the signature pad offers two modes. Draw works with a finger. Type renders your name in a script typeface and saves it as an image. The offer letter signing example shows a candidate choosing the typed option, and the signing record notes that he typed. Neither mode is stronger; the difference between them is explained in drawn versus typed signatures.

What does differ is what surrounds the mark. After a signing link, the finished PDF is certified so that any later edit invalidates its signature, and a separate certificate of completion lists your identity check, the signing time, your IP address, the moment you accepted consent and a hash of the document you were shown. The eIDAS Regulation’s article 26 describes an advanced electronic signature as uniquely linked to the signatory, capable of identifying them, created under their sole control, and linked to the data so any later change is detectable. A picture pasted onto a page meets none of those on its own.

When a phone signature is not enough

Some documents need more than any phone method gives. Deeds, documents that must be witnessed, and anything registered with a government body can have formal requirements that differ by jurisdiction. When the stakes are that high, ask the person who sent the document what form of signature they will accept before you sign.

For everything else, a practical rule: if you are only acknowledging something, markup is fine. If you are agreeing to terms that someone might later dispute, ask for, or send, a signing link. How to check what a signed file really contains is in how to check if a PDF is signed.

The table below compares the methods by what they need and what the finished file carries.

Common mistakes

Signing a photo of the document. A photo is not the PDF, and a photo of a signed photo is worse.

Reusing a saved signature image anywhere. A stored image is convenient and just as convenient for anyone else holding your phone.

Pinching and zooming to hit a tiny field. On a signing link, use the panel above the page.

Reloading halfway through. The session lives in the open page for thirty minutes, so a reload asks for your code again.

Build it

The sign on mobile page shows the compact signing layout step by step, and the draw or type signature page covers the pad. Signers need no app or account: the link opens in the phone browser, the page switches to compact mode below 560 pixels, consent is a required step, and one signature fills every spot assigned to that signer. Signing sessions last thirty minutes and are not stored, so a reload verifies again. To send a document so that someone else can sign it on their phone, follow the tutorial on sending a PDF for e-signature.