A contract hits your inbox between meetings. It needs a signature and a couple of comments, but the print-sign-scan routine doesn’t work from a phone. A powerful esign PDF tool handles both jobs, so you can mark up the document and add a legally recognized signature without finding a printer.
The best app depends on what you do most. A real estate agent signing leases between showings needs something different from a finance reviewer marking up statements, or an iPad user who wants Apple Pencil annotation. The platform matters too, and so does where your files live: Google Drive, Microsoft OneDrive, or only on the device.
TL;DR: quick picks
- Best overall for everyday mobile use: Lumin pairs PDF annotation and signing with native Google Drive and Microsoft OneDrive sync, plus a free plan, so a change made on your phone shows up on every device.
- Best for heavy markup and scanned files: Adobe Acrobat Reader has the deepest mobile annotation set and reliable OCR for turning scans into searchable text.
- Best for a polished iPhone or iPad experience: PDF Expert feels native on Apple hardware, with smooth Apple Pencil annotation.
Winners by use case
Best for signing on the go
If the main job is getting documents signed from a phone, you want a flow that does not force signers to create an account. Lumin Sign is best here for everyday use: it sends documents for signature, tracks status from a mobile dashboard, and lets recipients sign from any device with no account. Automated reminders chase signers who go quiet, and the status view shows who has opened, signed, or stalled, which matters when a closing waits on one missing initial. A finished signing leaves an audit trail, too, which is useful when finance or legal needs proof of who signed and when. eSignatures are recognized under UETA and the ESIGN Act, with equivalent laws abroad, so a signature captured on a phone holds up in most common business cases.
1 Lumin Sign: mobile signing plus tracking, free for up to 5 contracts a month, with paid plans for higher volume. Verified Digital Signing adds identity-checked signatures for high-assurance documents.
2 DocuSign: the heavyweight for signing at scale, with deep integrations and a mature mobile app. It fits enterprises with high volume and procurement requirements better than a solo signer.
3 Dropbox Sign: a clean, simple signing app, strongest when your files already live in Dropbox.
Best for annotating and marking up on the go
For comments, highlights, and review on a phone or tablet, you want fast markup and reliable syncing so notes are not stranded on one device. Lumin handles everyday annotation well: highlight, underline, strikethrough, comment, draw, and add text or images, with changes synced back to Google Drive or Microsoft OneDrive. Basic annotation is included in the free plan. Reliable two-way sync also avoids the version mess of emailing copies back and forth, where it is easy to comment on yesterday’s draft by mistake.
1 Lumin: everyday annotation with cross-cloud sync and a free plan. Raw text editing and advanced tools are paid, from around $9 a month. Its OCR is limited, so it is not the pick for marking up messy scans.
2 Adobe Acrobat Reader: the deepest mobile annotation set and dependable OCR, the better choice when you regularly annotate scanned pages.
3 Xodo: a capable free annotator with a light footprint on mobile.
Best for iPhone and iPad
On Apple hardware, a native feel and Apple Pencil support decide it. PDF Expert is the standout: built for iOS and macOS, with smooth Pencil annotation, fast rendering, and strong editing on the iPad. For anyone who reviews documents in meetings or signs with a stylus, the Pencil support and handwriting feel make it the most comfortable option on Apple devices.
1 PDF Expert: the most polished Apple-first experience for annotation and editing.
2 Lumin: a strong cross-platform alternative if you move between an iPhone, a work laptop, and the web, with cloud sync keeping everything current.
3 Adobe Acrobat Reader: reliable on iOS, especially when OCR matters.
Best for Android
Android users get the widest range of free, full-featured options. Xodo is a long-time favorite: free, fast, and capable for reading, annotating, and light editing on phones and tablets. Because Android hardware varies so widely, a lightweight app that stays quick on a mid-range phone is often worth more than a feature-stuffed one that stutters.
1 Xodo: a genuinely capable free annotator and reader on Android.
2 Adobe Acrobat Reader: strong Android annotation, with OCR on paid tiers.
3 Lumin: the pick when your Android signing and markup need to sync with Google Drive or Microsoft 365 across devices.
Best for Google Workspace and Microsoft 365 users
When documents live in cloud storage, the deciding factor is how cleanly an app opens, edits, and saves a file back without downloads and re-uploads. Lumin is strongest here: it integrates natively with both Google Drive / Google Workspace and Microsoft OneDrive / Microsoft 365, so a file opened from Drive on a phone syncs the changes straight back, with no manual re-upload. That native link removes the most common cloud headache: two people editing two downloaded copies and quietly overwriting each other’s work. More than 100 million people use the platform, and reviewers consistently single out the cloud workflow; Lumin holds 4.7 out of 5 on Capterra and 4.5 on G2.
#1 Lumin: native two-way sync with both Google and Microsoft clouds.
#2 Adobe Acrobat Reader: connects to cloud storage and works across platforms, though its home base is Adobe Document Cloud rather than native Drive or OneDrive editing.
Full comparison table
| Tool | Best for | Free plan | Edit PDF text | eSignature | Cloud (Google/Microsoft) | Pricing (from) |
| Lumin | Everyday sign + annotate with cloud sync | Yes: read, comment, draw, add text/images, basic sign | Paid | Yes (basic free; more on paid) | Native Google Drive + Microsoft OneDrive | Free; paid ~$9/mo |
| Lumin Sign | Mobile signing + tracking | Yes: up to 5 contracts/mo | n/a | Yes (UETA/ESIGN; VDS option) | Works with Google + Microsoft | Free up to 5/mo; paid |
| Adobe Acrobat Reader | Heavy markup + OCR | Yes: read, basic markup | Paid (Acrobat) | Paid | Adobe Document Cloud; connects to others | Paid |
| PDF Expert | iPhone and iPad experience | Limited | Paid | Limited | iCloud and connections | Paid |
| Xodo | Free Android annotation | Yes: full-featured | Limited | Limited | Cloud connections | Free; paid |
| DocuSign | Enterprise signing scale | Limited | n/a | Yes (enterprise) | Integrations | Paid |
| Smallpdf / iLovePDF | Quick one-off tasks | Yes: with caps or watermarks | Limited | Basic | Cloud connections | Free; paid |
Read the table by your dominant task, not by feature count. If you mostly sign, the eSignature and free-plan columns matter most. If you mostly annotate and your files live in the cloud, weigh the annotation tools against the cloud-sync column. Competitor pricing and free-plan limits change often, so confirm the current numbers on each vendor’s site before you commit.
FAQ
Can you sign a PDF from your phone? Yes. Mobile apps from Lumin Sign, Adobe, DocuSign, and others let you add a signature on a phone or tablet and send the signed file back, with no printing. Many flows let the recipient sign without creating an account. For low volume, Lumin Sign is free for up to 5 contracts a month.
Is there a free app to sign and annotate PDFs on mobile? Yes, several. Lumin’s free plan covers reading, commenting, drawing, adding text and images, and basic signing without watermarks. Xodo is free for annotation, and Adobe Acrobat Reader is free for reading and basic markup. Editing raw text or sending at a higher volume usually moves to a paid tier. Check each app’s free-plan limits before relying on it.
Can I edit a PDF directly in Google Drive on my phone? With the right app, yes. Lumin opens a PDF straight from Google Drive, lets you annotate or sign in the browser or app, and syncs the changes back to Drive without a manual re-upload. It offers the same native flow for Microsoft OneDrive.
Are mobile eSignatures legally binding? In most cases, yes. eSignatures are recognized under the ESIGN Act and UETA in the United States, with equivalent laws in the EU, the UK, Canada, India, Australia, New Zealand, and Singapore. Enforceability still depends on the document type and jurisdiction, so for high-stakes agreements, have a qualified attorney review the contract. This is general information, not legal advice.
What is the best PDF app for iPhone and iPad? For an Apple-native experience with Apple Pencil markup, PDF Expert is a common favorite. If you also work on a laptop or the web and want cloud sync across devices, Lumin is a strong cross-platform alternative.
Can I annotate a PDF offline on my phone? Yes, with apps that support offline mode. Lumin offers offline access and syncs your changes once you reconnect. Many competitors cache files for offline markup, too. Confirm offline support in the app’s settings, since some features still need a connection.
Is it safe to sign sensitive documents on a phone? With a reputable app, yes. Look for encryption and recognized compliance. Lumin uses AES-256 encryption and is SOC 2 Type 2 and GDPR compliant, and Lumin Sign offers Verified Digital Signing for identity-checked signatures. For regulated documents, confirm the provider meets your sector’s requirements.