You’ve got a PDF you need to mark up. Maybe it’s a contract that needs comments, a research paper you’re reviewing, or lecture notes where you want to highlight the parts that actually matter. Opening Adobe Acrobat and seeing that $22/month price tag is not the answer.
I tested 14 PDF annotation tools over three weeks to find the ones that let you highlight, comment, draw, and add sticky notes without paying a cent. Some are desktop apps, some run in the browser, and one comes built into your operating system. Here’s what actually works in 2026.
If you need full editing capabilities beyond just annotation, take a look at our roundup of the best free PDF editors – that covers text editing, page manipulation, and form creation. This guide focuses specifically on marking up and commenting on PDFs.
Quick Comparison Table
| Tool | Platform | Highlight | Sticky Notes | Drawing | Free Limit | Best For |
|---|---|---|---|---|---|---|
| Adobe Acrobat Reader | Windows, Mac, iOS, Android | Yes | Yes | Yes | Unlimited | Standard annotations everyone can open |
| PDF-XChange Editor | Windows | Yes | Yes | Yes | Unlimited (watermark on premium features only) | Power users who want 50+ annotation tools |
| Foxit PDF Reader | Windows, Mac, Linux | Yes | Yes | Yes | Unlimited | Cross-platform team annotation |
| Xodo | Web, iOS, Android | Yes | Yes | Yes | Unlimited | Mobile annotation and real-time collaboration |
| macOS Preview | Mac | Yes | No | Yes | Unlimited | Mac users who want zero installs |
| Okular | Linux, Windows | Yes | Yes | Yes | Unlimited | Linux users |
| Hypothes.is | Web (browser extension) | Yes | Yes (inline) | No | Unlimited | Academic collaboration and group annotation |
| Sejda | Web + Desktop | Yes | Yes | Yes | 3 tasks/day, 50 MB | Quick web-based markup |
Types of PDF Annotation
Before jumping into tools, a quick note on what “annotation” actually covers. PDF annotations are non-destructive markups – they sit on top of the document content without changing the underlying text or layout. When someone opens your annotated PDF in a compatible reader, they see your highlights, comments, and drawings as a separate layer.
The main annotation types you’ll use:
- Highlights – color-coded text highlighting (yellow, green, blue, pink, etc.)
- Sticky notes – clickable comment bubbles attached to a specific spot
- Text markup – strikethrough, underline, squiggly underline for proofreading
- Freehand drawing – pencil/pen tool for circling things or sketching
- Shapes – rectangles, circles, arrows, lines for callouts
- Stamps – “Approved”, “Draft”, “Confidential” badges
- Text comments – typed text placed directly on the page
Not every tool supports all of these. The table above covers the basics, but I’ll get into specifics for each tool below.
1. Adobe Acrobat Reader – The Default Choice
Look, I know it’s the obvious pick. But Acrobat Reader is free, it’s everywhere, and its annotation tools are genuinely solid. The paid features (editing text, converting formats, organizing pages) are locked behind the $22/month Pro subscription, but highlighting, commenting, drawing, and adding sticky notes? All free.
How to annotate
- Open your PDF in Acrobat Reader
- Click the Comment tool in the right panel (or the highlight icon in the floating toolbar)
- Pick your annotation type: highlight, underline, strikethrough, sticky note, text box, drawing, or stamp
- Select text to highlight it, or click anywhere to place a comment
- Save – annotations are embedded in the PDF file
What I liked
- Annotations made in Acrobat Reader are guaranteed to display correctly in other PDF viewers. Compatibility is basically 100%
- The comment panel on the right side lists every annotation in order – makes reviewing easy
- You can reply to other people’s comments, creating threaded discussions inside the PDF
- Color picker for highlights with custom colors, not just preset options
- Available on every platform including mobile, and annotations sync if you sign in
What’s annoying
- The installer tries to bundle McAfee or other software. Decline everything during setup
- It’s heavy. 500 MB+ install for what amounts to a viewer with markup tools
- Adobe constantly nudges you toward the paid plan with grayed-out Pro features
- On older machines, opening large PDFs (100+ pages) can lag
If you’re sending annotated PDFs to clients or colleagues and need to be sure they’ll see your comments correctly, Acrobat Reader is the safe bet. Everybody has it or can get it.
2. PDF-XChange Editor – Most Annotation Tools
This is the one I keep coming back to for heavy-duty annotation work. PDF-XChange Editor has somewhere around 50 different annotation and markup tools in the free version. Stamps, callouts, measurement tools, typewriter text, polygons, cloud shapes – it’s almost absurd how much they give away for free.
How to annotate
- Download PDF-XChange Editor (Windows only)
- Open your PDF
- Use the Comment tab in the ribbon for highlights, notes, text markup
- Use the Drawing tab for shapes, arrows, freehand, and stamps
- Right-click any annotation to change color, opacity, font, or line style
- File > Save to embed annotations
What I liked
- The sheer number of tools. I found annotation types I didn’t even know existed in the PDF spec, like “caret” annotations and polygon clouds
- You can customize the toolbar to show only the tools you use
- OCR is included free – so you can annotate scanned PDFs by first making them searchable
- Annotation summary can be exported as a separate document
- Keyboard shortcuts for switching between tools. Once you learn them, annotation speed doubles
What’s annoying
- Windows only. No Mac, no Linux, no web version
- Some features (like adding/removing pages or converting files) add a watermark on free tier. Annotation tools don’t, but it can be confusing to figure out which features are truly free
- The interface is dense. Lots of toolbars and panels that take time to learn
If you’re on Windows and you annotate PDFs regularly – reviewing contracts, grading papers, giving feedback on designs – PDF-XChange is the tool. Nothing else gives you this level of control at zero cost.
3. Foxit PDF Reader – Best Cross-Platform Option
Foxit has been Acrobat’s main competitor for over a decade, and their free reader includes a solid set of annotation tools. The big advantage: it runs on Windows, Mac, and Linux, and annotations created in Foxit display correctly in other PDF readers.
How to annotate
- Download Foxit PDF Reader for your OS
- Open the PDF and click the Comment tab
- Choose from: highlight, area highlight, underline, strikethrough, squiggly, note, typewriter, text box, callout, drawing tools
- Apply annotations, then save
What I liked
- Lighter than Acrobat Reader. Installs faster, opens PDFs faster, uses less memory
- Connected PDF feature lets multiple people annotate the same document and see each other’s comments in near real-time
- Area highlight is useful – you can highlight a rectangular region, not just text. Good for marking up images or diagrams in PDFs
- Spell check in text annotations
What’s annoying
- The Linux version hasn’t been updated in a while and feels dated compared to Windows/Mac
- Some features that look free have a 14-day trial timer. Annotation basics are always free, but the line between free and trial isn’t clear initially
- Foxit now pushes their cloud service pretty aggressively in the UI
If your team uses a mix of Windows, Mac, and Linux machines, Foxit is the pragmatic choice. Everyone gets the same annotation tools, and the files stay compatible.
4. Xodo – Best for Mobile Annotation
Xodo started as a mobile PDF app and it shows. The touch interface for annotating on tablets is the best I’ve used – smooth finger/stylus drawing, easy text selection for highlights, and gesture-based navigation between annotations. The web version works well too.
How to annotate
- Go to xodo.com or install the mobile app
- Upload or open your PDF
- Tap the pencil icon to enter annotation mode
- Use the bottom toolbar for highlights, underline, strikethrough, sticky notes, freehand drawing, text, shapes, and stamps
- Download or share when done
What I liked
- The mobile experience is genuinely good. If you read and annotate PDFs on an iPad or Android tablet, this is the one
- Real-time collaboration – share a link and multiple people can annotate simultaneously
- Freehand drawing with pressure sensitivity on tablets that support it
- No file size limits that I could find
- Annotations are standard PDF annotations, so they show up in any reader
What’s annoying
- You need to create an account now (they used to allow anonymous use)
- The web version sometimes has a slight delay when placing annotations on large files
- The free plan changed recently and some features that were free before now require Pro
For students reading textbook PDFs on a tablet, or anyone who needs to review documents on their phone during commutes, Xodo handles it better than the competition.
5. macOS Preview – Already on Your Mac
If you’re on a Mac, you already have a capable PDF annotator. Preview’s Markup toolbar covers the basics: highlights, text, shapes, signatures, and freehand drawing. No installs, no accounts, no nonsense.
How to annotate
- Double-click any PDF to open it in Preview (or right-click > Open With > Preview)
- Click the Markup icon in the toolbar (looks like a pen tip in a circle)
- Select text and right-click to highlight, underline, or strikethrough
- Use the toolbar for shapes, text boxes, signatures, and drawing
- Press Cmd+S to save
What I liked
- Zero setup. It’s there on every Mac, ready to go
- The drawing tools are smooth, especially with a trackpad or Apple Pencil on iPad (via Sidecar)
- Continuity Markup lets you annotate a PDF on your Mac using your iPhone or iPad as an input device
- Lossless saves – Preview doesn’t re-compress images or mess with the PDF structure
What’s annoying
- No sticky notes. You can add text boxes but they don’t collapse into a clickable icon like proper sticky notes do
- No comment panel listing all annotations. For heavily marked-up documents, this makes navigation harder
- Highlights sometimes don’t display correctly in non-Apple PDF readers
- No strikethrough highlight color options – it’s always red
Preview is perfect for light annotation – highlighting a few passages, adding a couple of notes, signing something. For serious review work with dozens of comments, you’ll want something with a comment panel.
6. Okular – Best for Linux
Okular is KDE’s document viewer, but it runs on any Linux desktop and has been ported to Windows too. Its annotation tools are more comprehensive than you’d expect from a default document viewer.
How to annotate
- Install Okular from your distro’s package manager (or Flatpak/Snap)
- Open the PDF and press F6 or go to Tools > Reviews
- The annotation toolbar appears with: pop-up note, inline note, freehand line, highlighter, straight line, polygon, stamp, underline, ellipse, typewriter
- Click to place annotations
- File > Save As to save with annotations embedded (important: regular Save stores annotations internally, Save As exports them into the PDF file)
What I liked
- Lightweight. Uses minimal resources even with 500+ page documents
- The annotation tools cover everything you need for document review
- Supports custom stamps – you can create your own approval/rejection stamps
- Tabbed interface for working with multiple PDFs
What’s annoying
- The Save vs. Save As distinction trips people up. If you just hit Save, annotations are stored in Okular’s internal database and won’t be visible when you open the file in another reader
- Text selection for highlighting can be finicky in multi-column PDFs
- Some annotation types (like typewriter text) look slightly different when opened in Acrobat
For the Linux crowd, Okular is the answer. Install it, annotate, export. If you need annotations to be compatible with Acrobat Reader users, just remember to use Save As instead of Save.
7. Hypothes.is – Best for Group Annotation
Hypothes.is is weird and cool. It’s a browser extension that lets you annotate any web page or PDF displayed in your browser. Your annotations live on the Hypothes.is server and can be public, shared with a group, or private. Academics love it for collaborative paper reviews.
How to annotate
- Install the Hypothes.is Chrome/Firefox extension
- Open a PDF in your browser
- Click the Hypothes.is sidebar icon
- Select text to highlight or annotate
- Type your comment and choose visibility: Public, group-only, or Only Me
- Other group members see your annotations in real-time when they open the same document
What I liked
- The collaboration model is unique. Create a group, share a PDF link, and everyone can annotate and reply to each other’s comments. Like Google Docs commenting but for PDFs
- Annotations are searchable across all documents you’ve ever annotated
- Used by hundreds of universities. If you’re in academia, your peers probably already have accounts
- Completely free for individuals and groups
What’s annoying
- No freehand drawing or shapes. Text-only annotations
- Annotations don’t embed in the PDF itself – they live on Hypothes.is servers. If you need to send an annotated PDF file to someone, this isn’t the tool
- Requires a browser. No desktop or mobile app
- The sidebar can interfere with some web-based PDF viewers
If you’re part of a reading group, academic review committee, or any team that discusses documents collaboratively, Hypothes.is does something that traditional PDF annotators can’t. But for individual annotation work where you need to save and share the file itself, look at the other tools on this list.
8. Sejda – Quick Web-Based Markup
Sejda is primarily known as a PDF editor, but its annotation tools work well for quick markup jobs when you don’t want to install anything. Upload, annotate, download. The free tier gives you 3 tasks per day with a 50 MB file size limit.
How to annotate
- Go to sejda.com and click “Annotate & Comment”
- Upload your PDF
- Use the toolbar for: text highlighting, strikethrough, underline, sticky notes, text boxes, freehand drawing, shapes, whiteout
- Click “Apply changes” and download
What I liked
- No signup required for basic use
- Files are deleted from servers after 2 hours
- The annotation tools are responsive and don’t lag even on larger files
- You can combine annotation with other edits (adding text, images) in one session
What’s annoying
- 3 tasks per day. If you’re annotating multiple documents, you’ll hit the wall fast
- 50 MB limit on free tier
- The “Apply changes” step flattens some annotation types, making them non-editable in other tools
Sejda fills the gap when you need to annotate a PDF right now, on someone else’s computer, without installing anything. For regular use, a desktop tool makes more sense.
Tips for Better PDF Annotation
After annotating hundreds of PDFs during testing, a few things stood out:
Use color coding consistently. Pick a system – yellow for questions, green for approved sections, red for issues – and stick with it. Most tools let you set a default highlight color so you don’t have to change it each time.
Write actionable comments. “Fix this” helps nobody. “Change the date from March to April per the updated contract terms” saves a round of back-and-forth. Takes five extra seconds, saves an email thread.
Check compatibility before sending. If you annotated in Preview on Mac, open the file in Acrobat Reader (or Chrome) to make sure everything looks right. Cross-reader rendering differences are real, especially with freehand drawings and stamps.
Flatten before archiving. If you need the annotated version to look identical everywhere, “flatten” the annotations (most editors offer this). Flattening burns the annotations into the page content, so they can’t be edited anymore, but they’ll display correctly in every viewer.
Need to do more than annotate? Our guide on filling PDF forms for free covers interactive forms, and the page numbers guide handles document preparation.
FAQ
Can I annotate a PDF for free without installing software?
Yes. Xodo and Sejda both run in the browser and offer highlighting, sticky notes, drawing tools, and text markup. Xodo has no file size limits on the free plan. Sejda limits you to 3 tasks per day and 50 MB per file. Both produce standard PDF annotations that open correctly in Adobe Reader.
Do annotations made in one PDF reader show up in another?
Usually yes, as long as both readers support the PDF annotation standard (ISO 32000). Annotations from Adobe Reader, Foxit, PDF-XChange, Xodo, and Sejda are interoperable. macOS Preview and Okular have occasional compatibility issues – Preview’s highlights sometimes don’t render in Windows readers, and Okular requires “Save As” to embed annotations in the file.
What’s the difference between annotating and editing a PDF?
Annotations sit on top of the document as a separate layer. They don’t change the original text, images, or layout. Editing means modifying the actual content – changing words, moving images, deleting paragraphs. Annotation is non-destructive and usually free. Full editing typically requires paid software or tools like LibreOffice.
Can I annotate a scanned PDF?
You can draw on it and add sticky notes, yes. But you can’t highlight text in a scanned PDF unless you run OCR first to make the text selectable. PDF-XChange Editor includes free OCR. For other tools, you’ll need to run the PDF through an OCR tool first, then annotate the resulting searchable PDF.
Is Adobe Acrobat Reader really free for annotations?
Yes. Highlighting, sticky notes, text markup (underline, strikethrough), freehand drawing, stamps, and text boxes are all free in Acrobat Reader. The paid Pro plan ($21.99/month) adds editing, page organization, file conversion, and form creation. If all you need is to mark up and comment on PDFs, the free Reader does the job.