How do I sign a PDF on my phone?

Built-in tools on each phone

iPhone: Markup

Markup is Apple's built-in annotation tool, baked into Mail, Files, Notes and Photos, and it handles PDF signing without installing anything. Open the PDF (an email attachment, a file in the Files app, or a scan), tap the Markup icon, a pen tip inside a circle, usually found in the share sheet or toolbar. Once Markup opens, tap the plus (+) button and choose "Signature." If you've signed something before, your saved signature appears and you can just tap it into place. If this is your first time, you'll draw your signature with your finger directly on the screen, which iOS then saves for next time so you're not redrawing it on every single document. Drag and resize the signature to sit correctly on the page, then save or share the signed file.

Android: no single built-in tool, but close options

Android doesn't have one universal signing tool the way iPhone does, since different phone makers build their own apps on top of Android. The closest thing most people already have is the PDF viewer inside the Google Drive app or Google's Files app, both of which include a basic markup or "fill and sign" option for drawing directly on a page. Samsung phones with an S Pen add their own Notes-based PDF markup. Because this varies by device, the more reliable free route on Android is installing a dedicated app rather than hunting for whatever your specific phone happens to include, covered next.

Apps and when they fall short

When the built-in option is missing, awkward, or you want one consistent experience across iPhone and Android, the free Fill & Sign feature inside Adobe Acrobat Reader, Adobe's free PDF app, is the most reliable option. Acrobat Reader itself is free to download on both platforms, and its Fill & Sign tool lets you type, draw, or upload an image of your signature and drop it anywhere on the page, the same basic idea as iPhone's Markup but consistent across any phone. According to Adobe's own description of the tool, it's built for "simple workflows that require you to add your own signature, initial a page, or request a signature from one or a few parties," which is exactly the phone-signing use case this article covers.

Where both Markup and the free Acrobat app fall short is the same place: they're built for you signing something yourself, not for sending a document to someone else and getting proof back that they specifically signed it. Neither one manages signing order if more than one person needs to sign, neither sends an automatic reminder if someone forgets, and neither produces a real audit trail, the timestamped, IP-logged record that shows exactly who signed, when, and from where. A signature drawn with Markup is visually a signature, but it's just an image placed on a PDF; nothing records that the specific named person placed it there on that specific date under an agreement to sign electronically. For your own quick paperwork, that distinction rarely matters. The moment it's someone else's signature you're collecting, it starts to.

Common problems signing on a phone, and the fix

• The PDF won't open in Markup at all. This usually means it opened in a different app's preview instead of the Files or Mail viewer that exposes the Markup toolbar. Save the attachment to Files first, then open it from there, which reliably surfaces the Markup icon.
• Your signature looks shaky or too large. Finger signatures on a small screen are genuinely harder to control than a mouse or a real pen. Draw it slower than feels natural, and don't worry about making it look exactly like your paper signature, what matters legally is intent to sign, not a perfect visual match to your usual handwriting. A cleaner image is possible, as in making a signature image from a photo.
• Android's built-in option is greyed out or missing entirely. This is common on phones where the default PDF viewer isn't Google's own, some manufacturers set a different default app that has no markup feature at all. Installing the free Adobe Acrobat Reader app and setting it as your default PDF viewer fixes this reliably across any Android phone.
• You need to sign the same spot on a recurring form every month. Both Markup and Acrobat Reader remember your saved signature, so the actual drawing step only happens once. What doesn't carry over automatically is the placement on the page, you'll still need to drag it into position each time on a built-in tool, which is exactly the kind of repetitive step a template feature in a dedicated e-signature tool removes.

A quick worked example

Say your landlord emails a one-page lease renewal and asks you to sign and send it back today. On an iPhone: open the email, tap the attachment to preview it, tap the share icon, choose Markup (or tap the Markup icon directly if it's already showing in the preview toolbar), tap the plus button, select Signature, draw it once, drag it into the signature line, tap Done, then share the signed file back as a reply attachment. Total time once you've done it before: under a minute. On Android without a reliable built-in option: save the attachment, open it in Adobe Acrobat Reader, tap the Fill & Sign icon, draw and place your signature the same way, then share the completed file. Either way, for a simple one-page renewal you're signing yourself, this is genuinely the fastest path, faster than printing anything or opening a separate e-signature tool for a document nobody else needs to sign. Email attachments are covered in signing from Gmail or Outlook without printing.

When the other side needs a proper e-signature record

If you're the one signing a document someone else sent you, built-in tools are usually fine, the sender's e-signature tool is what generates the real record, not your phone. The question that matters is the reverse: when you're the one sending a document to a customer, a vendor, a new hire, and you need proof later that they actually agreed to it. That's when a dedicated e-signature tool earns its cost over a free phone app. A tool built for this sends the recipient a secure signing link, requires no account from them, and automatically produces a timestamped audit trail, who opened it, when, from what IP address, when they signed, all bundled with the completed document. Several tools cover this at low or no cost for occasional use; my guide to getting a document signed online walks through the actual steps and the free tiers available, and it's worth five minutes to set up properly rather than relying on a photo of a signature for anything that matters. On a computer instead, see signing a document on a Mac or Windows PC.

A genuinely common edge case worth flagging: signing something on your own phone using Markup, then forwarding that signed PDF to someone else as your "signature" on an agreement between you. This technically works and is legally recognized in most contexts in the US under the ESIGN Act and the state-level UETA laws, provided both sides intend to transact electronically, but you're trading away the audit trail entirely. If the other party ever disputes that you signed it, or disputes when, you have far less to point to than you would with a proper e-signature record. For a low-stakes form, that's an acceptable trade. For a contract with real money or obligations attached, it isn't, and that's the actual line I'd draw.

How I'd approach this

I use Markup constantly for my own quick paperwork, initialing a form, signing something that's genuinely low-stakes, and there's no reason to overcomplicate that. Where I see small business owners get this wrong is using the exact same casual approach for documents where it actually matters, a client service agreement, a vendor contract with payment terms attached, something that could end up disputed. The fix isn't a complicated tool, it's picking the right one for the specific document in front of you: your phone's built-in signature for your own low-stakes signing, a real e-signature tool the moment you're collecting someone else's signature on anything that carries actual weight. When a client needs their entire document and contract flow built properly, matched to how their business actually operates rather than cobbled together from whatever app is free that week, that's the kind of system I build. Get in touch if that's where you're at.