Someone sends you a document to sign while you're away from your desk. You have your phone. You don't want to print, sign, scan, and email โ and you shouldn't have to. Signing a PDF on a phone is genuinely straightforward in 2025, whether you're on iPhone or Android. Here's exactly how to do it.
Signing a PDF on iPhone
iPhone has a built-in PDF signing capability through the Markup tool โ no app download required.
- Open the PDF in Files, Mail, or any app that shows a share icon
- Tap the share icon, then tap Markup โ or if viewing in Files, tap the pencil icon in the top right corner
- In Markup, tap the + button at the bottom right and choose Signature
- Draw your signature with your finger โ or use an Apple Pencil on iPad for a more precise result
- Tap Done, then drag the signature to the correct location on the document and resize as needed
- Tap Done again to save, then share the signed PDF by email or message
iPhone stores your saved signatures so you don't have to redraw them every time. Once you've created a signature, it appears as an option each time you open the Markup signature tool.
Signing a PDF on Android
Android doesn't have a universal built-in PDF signing tool the way iOS does, but several options work well:
- Adobe Acrobat (free): open the PDF in Acrobat, tap the pencil icon, choose Fill & Sign, tap the signature icon, draw your signature, and place it on the document. Acrobat saves your signature for future use.
- Google Drive: if the PDF is in Google Drive, open it and use the pen icon to annotate. The annotation tools include a drawing option you can use to draw a signature, though it's more basic than dedicated signing apps.
- Browser-based tools: WukongPDF at www.wukongpdf.com works in Android browsers. Open the site, upload the PDF, use the signature tool to draw with your finger, position it, and download the signed version.
What Type of Signature Does This Create?
The methods above create an electronic signature โ specifically, a drawn signature image placed on the document. This is legally valid in most countries for most types of agreements under electronic signature laws (eSign Act in the US, eIDAS in the EU). It's not the same as a certified digital signature with cryptographic verification, but for the vast majority of everyday business documents โ employment contracts, service agreements, consent forms, rental agreements โ it's legally sufficient.
If the document requires a certified Sign PDF with audit trail and identity verification โ financial instruments, notarized documents, certain legal filings โ use a dedicated e-signature platform like DocuSign or Adobe Sign, which provide the authentication layer that a drawn signature doesn't.
Tips for a Clean Signature on a Small Screen
- Use your fingertip, not your fingernail โ fingertip contact gives more consistent line width
- Sign slowly โ phone screens respond to touch speed, and slower movement usually produces cleaner lines
- Sign in landscape orientation for more horizontal space
- If the signature looks wrong, clear it and try again before placing it on the document
Saving and Returning the Signed Document
After signing, save the PDF to your device or cloud storage before sharing. On iPhone, the signed PDF saves automatically when you tap Done in Markup โ share it from Files or the app you opened it in. On Android, download the signed version from whichever tool you used, then attach it to an email reply. Keep a copy of the signed document for your own records alongside sending it โ the document with your Sign PDF on it is a record of your agreement, not just something you forward and forget.