Best Apps to Sign PDF Documents from Your Phone

Signing a PDF document from your phone isn’t a luxury anymore — it’s a necessity. I sign contracts, invoices, and official documents directly from my phone, without printing or scanning anything. I’ve tested practically every digital signature app on the market, and here I present the best options both free and paid, with their real advantages and limitations.

Table of contents

Best free apps for signing PDFs

If you only need to sign documents occasionally, these free apps are more than enough:

Adobe Acrobat Reader

Adobe Acrobat Reader is the de facto standard for PDF and its signature function is very good. You can create your signature by drawing it with your finger, writing it in typography, or taking a photo of your signature on paper.

What I like about Adobe is that the signature is saved as a vector, which looks much more professional than a blurry photo. Plus, it’s compatible with digital certificates if you need legally valid signatures.

The free version lets you sign and fill forms. For advanced features like sending documents for electronic signature or editing PDFs, you need the Pro version.

Xodo PDF

Xodo is my favorite app for signing PDFs because it’s completely free with no limitations. You can sign, add text, highlight, and annotate without paying anything.

The interface is clean and fast. Xodo also syncs with Google Drive, Dropbox, and OneDrive, which is very convenient if you receive documents by email and save them to the cloud.

Foxit PDF

Foxit is another excellent app with free signing. It has more features than Xodo in its free version, including the ability to create fillable forms and add watermarks.

Pro-tip: If you just need to sign PDF documents without complications, Xodo is the best free option. It’s fast, reliable, and without annoying ads.

Paid apps for professional signing

If you need legally valid electronic signatures or advanced features, these paid apps are the best:

DocuSign

DocuSign is the undisputed leader in professional electronic signatures. It lets you send documents for signature to multiple people, real-time tracking, and legally valid signatures in most countries.

The personal plan costs about $10/month and is sufficient for individual professional use. Companies typically need higher plans that include templates, integrations, and user management.

Adobe Sign

Adobe Sign is integrated into the Adobe ecosystem and works great if you already use Acrobat, Creative Cloud, or Document Cloud. The electronic signature is legally binding and Adobe integration is unbeatable.

SignNow

SignNow is a more affordable alternative to DocuSign with similar features. It costs around $8/month in the basic plan and offers legally binding electronic signatures, templates, and tracking.

HelloSign (Dropbox)

HelloSign, now integrated into Dropbox, is another interesting option if you already use Dropbox. The signature is legally binding and Dropbox integration greatly facilitates the workflow.

Comparison table of PDF signing apps

The main difference between free and paid apps is the legal validity of the signature. If you sign important contracts, you need an app with advanced electronic signature like DocuSign or Adobe Sign.

How to sign a PDF step by step (using Xodo as example)

I’ll use Xodo as an example because it’s free and works very well:

1. Download Xodo PDF from Google Play or App Store.
2. Open the PDF document you want to sign (from email, cloud, or storage).
3. Tap the edit icon (pencil) in the toolbar.
4. Select “Signature” or “Create signature.”
5. Draw your signature with your finger on the screen.
6. Adjust the size and place it where it belongs on the document.
7. Save the signed document.

For a more professional signature:

1. Before drawing, adjust the stroke width so it looks like a pen signature.
2. Use the “Saved signature” option so you don’t have to draw every time.
3. If you have a stylus (S Pen, Apple Pencil), use it for greater precision.

Digital certificate signature vs. simple electronic signature

It’s important to understand the difference because not all signatures have the same legal validity:

Simple electronic signature

This is the one you make by drawing with your finger on the screen. It has legal validity in many contexts, but is hard to verify and can be legally challenged.

Advanced electronic signature

Uses a digital certificate that guarantees your identity. This is the signature you need for official documents, high-value contracts, and government procedures.

Qualified electronic signature

The highest level, equivalent to a handwritten notarized signature. Can only be obtained with digital certificates issued by recognized trust service providers.

Warning: For contracts of significant importance or government procedures, always use advanced or qualified electronic signature. A simple signature drawn with your finger may not be sufficient in case of legal dispute.

Security when signing PDFs from your phone

Signing documents from your phone is convenient, but there are risks you should know about. Not all documents are equal and not all security measures are sufficient:

Always verify the document before signing: It sounds obvious, but many people sign without reading. On mobile it’s easier to do because the screen is small and we tend to scroll quickly. Take your time to review every page of the document before adding your signature. I’ve seen cases of people signing contracts with hidden clauses because they didn’t read everything.

Protect signed documents with a password: After signing a PDF, many apps let you password-protect it. This is especially important if the document contains sensitive data like bank account numbers, ID numbers, or tax information. In Xodo, for example, you can save the PDF with a password from the options menu.

Be careful with public WiFi: If you’re signing sensitive documents, avoid doing so on public WiFi networks. Use your mobile data connection or a VPN. An attacker on the same network could intercept the document.

Keep backup copies: Signed documents are important. Save them in at least two places: one in the cloud (Google Drive, Dropbox) and another locally on your phone or external hard drive. If you lose your phone, you won’t lose your signed documents.

Tip: Set up automatic screen lock on your phone with a PIN or fingerprint. If you lose your phone, no one can access your signed documents without your authentication.

FAQ: Frequently Asked Questions

Does a signature from my phone have legal validity?

Yes, in most countries electronic signatures have legal validity. The level of validity depends on the signature type (simple, advanced, or qualified). The advanced signature with digital certificate is the most legally secure.

Can I sign a PDF sent to me via WhatsApp?

Yes. Save the PDF to your phone, open it with a signing app (Xodo, Adobe, etc.), sign it, and save it. Then you can share it back via WhatsApp, email, or any other channel.

Do I need a stylus to sign?

No, you can sign with your finger, but a stylus (S Pen, Apple Pencil, or any capacitive stylus) gives much more precise and professional results. If you sign documents frequently, it’s worth investing in one.

Can I save my signature so I don’t have to draw it every time?

Yes, all apps mentioned let you save your signature for reuse. It’s a basic feature that saves a lot of time if you sign multiple documents daily.

Conclusion

Signing PDF documents from your phone is fast, easy, and legally valid. For occasional use, free Xodo or Adobe Acrobat Reader are more than enough. For professional use with legal validity, DocuSign or Adobe Sign are the most reliable options. My personal recommendation: start with Xodo to see if it works for you, and if you need more, move to DocuSign. Stop printing documents to sign them — your phone does the same in seconds.