PDF reader for iPhone — annotate and sign on iOS

Why the built-in tools are usually enough

iOS has had a Markup annotation layer since iOS 9 in 2015, and a dedicated Files app with full PDF viewing since iOS 11 in 2017. The combination handles highlighting, drawing with finger or Apple Pencil, text annotation, shape annotation, signature placement (with saved signature reuse), page rotation, page deletion, page reordering, and form fill — all without installing a third-party app.¹ The Files app integrates with iCloud Drive, Google Drive, Dropbox, OneDrive, SMB shares, and local downloads; the same PDF is accessible from every app on the device through the standard iOS document picker.

On iPad, the Markup experience is even better — the Apple Pencil draws directly on the page with palm rejection, Scribble converts handwriting in form fields to typed text, and Stage Manager / Slide Over allow side-by-side PDF review with another app. For 90% of personal iPhone and iPad use, no additional app is required.

What the built-in iOS PDF stack actually does

Eight features worth knowing about, all available without installing anything:

Seven iPhone PDF readers compared

Detailed take on each reader

Files + Markup — the built-in default

The Files app is the home of every PDF on your iPhone, and Markup is the annotation toolbar that lives inside it. Tap a PDF, tap the Markup pencil-in-circle icon top right, and the toolbar appears with pen, highlighter, eraser, ruler, lasso, shapes, text, signature, and undo. The signature feature is particularly good — you can store multiple signatures (drawn with a fingertip, captured via the camera, or drawn with Apple Pencil) and reuse them across documents. The system carries the same Markup behaviour into Mail attachments, Books, Notes, and Photos.

Apple Books — for long-form reading

Books is a competent secondary PDF viewer focused on long-form reading. It supports highlights and notes, page-flipping animation, library-style management alongside ebooks, and reads aloud (text-to-speech). What it does not have: signature placement, draw tools, or form fill. For users with a lot of PDFs alongside an ebook library, Books is the right app to read them in; for active annotation or signing, Files+Markup is the right app.

PDF Expert — the iPad annotator favourite

PDF Expert by Readdle is the most-polished commercial PDF reader on iOS, especially on iPad. The free Reader tier gives you tabbed multi-document UI, customisable highlight palettes, a more comprehensive annotation toolset than Markup, and a sidebar for quick page navigation. The paid Pro tier ($79.99/year) adds editing, OCR, redaction, and page management. For users who annotate hundreds of pages a year on an iPad with Apple Pencil, PDF Expert is materially better than Markup.

Adobe Acrobat Reader — Liquid Mode plus corporate

Adobe Reader on iOS has two genuinely useful features. First, Liquid Mode reflows PDF content to mobile screen width — text wraps, fonts grow, layout is rebuilt for small screens. Brilliant for long-form text PDFs on iPhone, useless for forms or charts. Second, the Adobe Sign integration handles request-a-signature workflows from corporate counterparties. For everyone else, the resource cost and Adobe Document Cloud push are not worth it.

Xodo — the free cross-platform reader

Xodo (now Apryse) is a polished cross-platform PDF reader that works the same on iOS, Android, and web. The free tier handles annotations, form fill, and signatures without locking core features behind a paywall. For users who switch between an iPhone and an Android phone or want consistent behaviour on a Chromebook, Xodo is the natural pick.

GoodReader — the power user choice

GoodReader has been around since the iPad launched and remains the favourite of users with very large PDF collections. It offers powerful file management (folders, tags, sync to remote servers via WebDAV/SFTP/SMB), advanced annotation, and a customisable touch UI. The trade-off is a one-time purchase (~$5.99) and a learning curve. For users with hundreds of PDFs organised in deep folder structures, GoodReader pays for itself in time saved on navigation.

ScoutMyTool in mobile Safari

For active edits Files + Markup cannot do — signing into a specific position with precise control, watermarking, page numbering, merging, splitting, compressing, filling AcroForm fields — ScoutMyTool's browser tools work in mobile Safari on iPhone and iPad with zero install. Each tool runs client-side in the Safari tab using pdf-lib; the PDF never leaves your device. Useful as the "second tool" alongside Files + Markup for everyday reading.

Which one to install — short decision tree

1. Read PDFs occasionally? Files + Markup is enough. Do not install anything.
2. Annotate heavily on iPad with Apple Pencil? Install PDF Expert. Free tier alone is excellent.
3. Read long-form text PDFs (academic papers, ebooks) on iPhone? Install Adobe Reader for Liquid Mode. Use it only for that.
4. Need cross-platform parity with Android / Chromebook? Install Xodo.
5. Manage hundreds of PDFs with custom folders + remote sync? Buy GoodReader. One-time fee, no subscription.
6. Need to actively edit (watermark, merge, split, compress)? Bookmark ScoutMyTool in Safari. Browser-only, no install, no upload.

Related ScoutMyTool tools and articles

• All free PDF tools — browser-based toolbox that works in mobile Safari.
• Sign PDF — sign without installing a desktop or mobile app.
• Add Watermark — confidentiality or "draft" stamps.
• Merge PDF — combine PDFs in the browser.
• Compress PDF — shrink a PDF before sending via email or Messages.
• PDF Form Fill — fill AcroForm fields without an app.
• How to e-sign a PDF on iPhone — sister piece on the signing flow specifically.
• PDF reader for Android — sister piece for the Android side.
• Best PDF reader for Mac — companion piece for the Mac side.

Frequently asked questions

Do I need to install a PDF reader on my iPhone at all?

For most users, no. iOS has had a competent built-in PDF viewer in the Files app since iOS 11, with the Markup tool layer providing highlighting, drawing, text annotations, and signature placement. The same Markup runs over PDFs in Mail attachments, Books, Notes, and Photos. For 90% of personal use cases — reading a receipt, annotating a contract, signing a school form — installing a third-party app adds friction without adding capability.

When is PDF Expert worth installing?

When you annotate many PDFs a week and want a more polished experience than Markup provides — particularly on iPad. PDF Expert offers tabbed multi-document UI, customisable highlight colours, more annotation tools, side-by-side PDF viewing, and OCR (in the paid Pro tier). The free Reader tier alone is genuinely useful and replaces Markup for heavy users. The paid Pro tier ($79.99/year as of May 2026) adds editing, OCR, page management, and redaction — overlap with what ScoutMyTool browser tools provide for free.

Is Adobe Acrobat Reader worth installing on an iPhone?

Only if you actively work with Adobe-pipelined documents (Adobe Sign workflows, corporate review packets sent from Acrobat Pro). Adobe Reader on iOS is heavier than the alternatives and pushes Adobe Document Cloud aggressively during sign-up. The one genuinely-useful feature unique to Adobe Reader is Liquid Mode, which reflows PDF content to fit the iPhone screen — text wraps, fonts grow, layout is abandoned. Great for long-form text PDFs on a small screen; bad for layout-sensitive documents (forms, charts, multi-column briefs).

How do I share an annotated PDF from iPhone?

Markup's share button respects everything iOS shares: AirDrop, Mail, Messages, save back to iCloud Drive, save to Files, save to Google Drive / Dropbox / OneDrive if you have those apps. For sensitive material, password-protect the PDF first using ScoutMyTool's Protect PDF tool in Safari, then send the password through a separate channel. The "share annotated PDF" flow is identical whether you used Markup, PDF Expert, Adobe Reader, or any other app — they all hand off to the iOS share sheet at the end.

Are iPhone PDF readers safe with confidential documents?

All built-in iOS tools (Files / Markup / Books / Notes) process documents entirely on-device — nothing is uploaded to Apple beyond the iCloud Drive sync if the file lives in iCloud, and that sync is end-to-end encrypted under Advanced Data Protection (an opt-in setting). Third-party readers vary: PDF Expert and Xodo respect iCloud and do not push their own cloud aggressively; Adobe Reader and Foxit push their own cloud accounts. ScoutMyTool in Safari runs client-side in the browser tab with no upload at all. For maximum privacy on iPhone, stick to built-in tools and ScoutMyTool, and avoid signing into vendor cloud accounts unless you actually need them.

How do I get a PDF onto my iPhone in the first place?

Four common paths. (a) Email attachment — tap the PDF in Mail to open in Markup. (b) Files app — connect to iCloud Drive, Google Drive, Dropbox, OneDrive, or a local SMB share; browse to the PDF. (c) Web download — tap a PDF link in Safari, choose "Open in" or download to Files. (d) AirDrop from another Apple device — accept the share and choose where to save. All four end up with a PDF in the Files app, where every iOS PDF reader can find it.

Can I scan a paper document to PDF on my iPhone?

Yes, with built-in tools. The fastest path is the Notes app: open Notes, tap the camera icon, choose "Scan Documents". The camera turns into a document scanner that detects page edges, captures a high-resolution photo, applies a perspective correction, and lets you scan a second page. When you tap Save, the result is a multi-page PDF saved to the note. From there, export to Files for any other reader. The Files app itself also has a scan option in the +(plus) menu in some iOS versions. No third-party app is required for everyday scanning.