How to Add Comments to a PDF Document

Annotating a PDF is one of those tasks that sounds simple until you're staring at a document with no obvious way to leave a note. The good news: PDF commenting is well-supported across platforms and tools — but how you do it depends significantly on which software you're using, what device you're on, and what kind of comment you actually need to leave.

What "Adding a Comment" to a PDF Actually Means

In PDF terminology, comments and annotations are often used interchangeably, but they cover a range of markup types:

• Sticky notes — floating text boxes attached to a specific point in the document
• Text highlights — colored overlays on selected text, often paired with a note
• Strikethrough and underline — markup indicating edits or emphasis
• Text boxes — freestanding typed text placed directly on the page
• Drawing tools — freehand markup, arrows, shapes
• stamps — predefined or custom labels like "Approved" or "Draft"

Most PDF tools support at least the first two. Full annotation suites — including stamps, drawing tools, and comment threading — are typically found in more capable desktop applications.

How to Add Comments in Adobe Acrobat (Reader and Pro)

Adobe Acrobat Reader (the free version) supports basic commenting. Here's the general workflow:

1. Open your PDF in Acrobat Reader
2. Navigate to Tools > Comment or click the comment icon in the toolbar
3. Select your annotation type — sticky note, highlight, underline, etc.
4. Click or select text in the document to place the comment
5. Type your note in the pop-up text field
6. Save the file

Adobe Acrobat Pro expands this with redaction tools, comment tracking, reply threads, and the ability to export comment summaries — useful for document review workflows involving multiple reviewers.

📝 Note: Not all PDFs accept comments. Documents with security restrictions set by the creator may block annotation entirely, regardless of the software you're using.

How to Add Comments in a Web Browser (Chrome, Edge, Firefox)

Modern browsers can open PDFs natively, but their built-in PDF viewers are typically read-only — they don't support annotation. If you open a PDF in Chrome or Edge and want to leave comments, you'll need to either:

• Use a browser extension with PDF editing capabilities
• Download the file and open it in a dedicated app
• Upload it to a cloud-based PDF tool

This is a common point of confusion: just because your browser displays a PDF doesn't mean it can annotate it.

How to Add Comments on Mac (Preview)

macOS includes Preview, which handles basic PDF annotation without any additional software:

1. Open the PDF in Preview
2. Click View > Show Markup Toolbar (or the pencil icon in the toolbar)
3. Use the tools to add highlights, notes, shapes, or text
4. Save with File > Save (or export as a new PDF)

Preview is capable for personal use and light review work, but it lacks advanced features like comment threading or export summaries.

How to Add Comments on Windows (Without Adobe)

Windows doesn't include a built-in PDF annotator the way macOS does. Common alternatives include:

Microsoft Edge's built-in PDF viewer has improved in recent versions and now supports basic highlights and notes — a workable option for quick markups without installing extra software.

How to Add Comments on Mobile Devices 📱

iOS: The Files app and Mail app can open PDFs with basic markup using Apple's built-in markup tools. Tap the pen icon to access highlights, text, and drawing tools. Apps like Adobe Acrobat Mobile offer more complete annotation support.

Android: Android doesn't have a universal built-in PDF annotator. Adobe Acrobat, Xodo, and similar apps fill this gap. Functionality varies between apps — some free tiers limit how many comments you can save or export.

Cloud-Based PDF Commenting (Google Drive, Dropbox, Office 365)

If your PDF is stored in a cloud service, you may have annotation options without installing anything:

• Google Drive can display PDFs but doesn't natively annotate them — you'd need Google Docs (which converts the PDF, sometimes imperfectly) or a connected app
• Dropbox offers basic annotation in its web viewer on certain plan tiers
• Microsoft 365 includes annotation in its online PDF viewer within Edge and the Office apps, depending on your subscription

Cloud tools are convenient for collaboration, but comment fidelity (how reliably comments are preserved when a file moves between platforms) can vary. A comment added in one tool doesn't always appear correctly when opened in another.

Factors That Shape Your Experience

The practical experience of adding comments to a PDF shifts depending on several variables:

• PDF version and security settings — creator-applied restrictions can block editing entirely
• Operating system — macOS users have Preview; Windows users need a third-party tool or Edge
• Device type — desktop tools offer more precision; touchscreen annotation on mobile can feel limited without a stylus
• Collaboration needs — single-user markup vs. tracked multi-reviewer annotation are meaningfully different use cases
• File size and complexity — heavily formatted or scanned PDFs may behave differently across tools

Whether the free tier of a given tool covers what you need, or whether a paid application is warranted, comes down to how frequently you annotate, the complexity of your review workflows, and the platforms your collaborators are using.