How to Add Comments and Sticky Notes to a PDF

You've got a PDF. Maybe it's a contract, a design proof, or a draft report someone sent you. You need to leave feedback — "move this paragraph," "wrong number here," "can we rephrase this?" — but you don't want to actually change the document itself. You want to mark it up. Leave notes. Point at things and say "fix this."

That's what PDF comments and sticky notes are for. They sit on top of the document like Post-it notes on a printed page. The original content stays untouched, but your feedback is right there, attached to the exact spot that needs attention.

It sounds straightforward, and honestly, it should be. But depending on the tool you're using, it can be anywhere from dead simple to surprisingly annoying. Let's walk through the options that actually work.

Why Comments Beat Email Chains

Before we get into the how, let's talk about why this matters. I've watched teams go back and forth over email — "on page 3, the second paragraph, third line, the word 'approximately'..." — when they could have just dropped a sticky note directly on the word.

PDF comments solve the "which part are you talking about?" problem. Instead of writing a separate document full of references, your feedback lives right where it belongs. Everyone looking at the file sees the same notes in the same places.

This is especially useful for:

Contract reviews. Your legal team can flag clauses that need changes without creating a separate redline document. The comments sit right next to the language in question.

Design feedback. When someone sends you a mockup as a PDF, you can circle the element that's off and say exactly what's wrong with it. Way better than "the thing on the left looks weird."

Academic papers. Peer review on a PDF is standard practice, and sticky notes are how most reviewers leave their thoughts. Highlighting plus a note in the margin — that's the workflow.

Any approval process. If you need sign-off on a document, comments let the reviewer say "approved with changes" and actually show what those changes are.

Method 1: Add Comments to a PDF Online

The fastest way to annotate a PDF is with a browser-based tool. No software to install, no account to create — just upload, comment, download.

OnlyDocs lets you open any PDF and add comments directly in your browser. Click anywhere on the page, type your note, and it attaches to that spot. You can also highlight text and add a comment to the highlight, which is great for calling out specific wording.

Here's the basic process:

1. Go to onlydocs.net and open your PDF
2. Select the comment or sticky note tool from the toolbar
3. Click the spot on the page where you want to leave your note
4. Type your comment and save it
5. Download the annotated PDF when you're done

The comments are embedded in the PDF file itself, so anyone who opens it in any PDF reader will see them. That's important — your notes aren't trapped in some proprietary format. They follow the PDF standard, which means they'll show up in Adobe Reader, Preview, Chrome's built-in viewer, whatever.

Online tools work well for quick feedback rounds where you have a handful of comments. If you're doing deep markup on a 200-page document, you might want something with a bit more horsepower. But for most people, most of the time? This is the move.

Method 2: Using Adobe Acrobat Reader (Free)

Adobe Reader is free, and it handles comments just fine. You don't need the paid Acrobat Pro for basic annotation — that's a common misconception.

Open your PDF in Reader, and look for the comment tools in the right sidebar or toolbar. You'll find sticky notes, text highlights, strikethrough, underline, and a drawing tool. The sticky note is probably what you'll use most. Click where you want it, type your note, and it appears as a small icon on the page. Click the icon to read the full comment.

One thing worth knowing: Adobe Reader lets you reply to comments. So if someone sends you an annotated PDF, you can respond to their notes directly, creating a threaded conversation inside the document. It's actually pretty useful for back-and-forth reviews.

The downside is that Reader is desktop software, so you need to install it. It's also heavy — it takes a while to load and uses a lot of memory. For just adding a couple of sticky notes, it's overkill. But if you already have it installed, it works.

Method 3: macOS Preview

If you're on a Mac, Preview handles PDF comments natively and it's already on your computer. Open the PDF, click the markup toolbar button (it looks like a pen tip), and you'll see options for text notes, shapes, highlights, and more.

Preview calls its sticky notes "Notes" — click the note icon, then click on the page. A yellow box appears where you can type. It's minimal but functional.

Fair warning: Preview's annotation tools are basic. You get notes and highlights, but there's no threaded replies, no comment filtering, and the interface isn't really designed for heavy markup. It's fine for quick notes on a one-pager. For serious review work, you'll want something else.

Method 4: Browser-Based PDF Viewers

Chrome, Edge, and Firefox all have built-in PDF viewers, and recent versions have started adding annotation features. Chrome and Edge now let you highlight text and add basic notes directly in the browser tab.

This is convenient because there's literally nothing to set up. You open a PDF, and you can start marking it up. But the feature set is limited compared to dedicated tools. As of early 2026, browser viewers handle highlights and basic text notes, but they're missing things like drawing tools, stamps, and comment threading.

Types of PDF Comments (and When to Use Each)

Not all annotations are created equal. Here's a quick rundown of the main types:

Sticky notes are the workhorse. They're small icons that expand to show your full comment. Use them for general feedback, questions, or suggestions that apply to a specific area of the page.

Text highlights with comments are better when you're reacting to specific words or sentences. Highlight the text, attach a comment explaining your thought. The reader immediately sees what you're referring to.

Strikethrough and insertion markup are for when you want to suggest specific text changes. Strike through the words that should be removed, use an insertion caret to show where new text should go. This is the closest thing to "track changes" in a PDF.

Drawing markup — rectangles, circles, arrows — works well for visual content. If you're reviewing a layout or diagram, circling an element and adding a note is the clearest way to communicate.

Text boxes put your comment directly on the page surface rather than hiding it behind an icon. These are good for short, important notes that you want to be immediately visible, but they can clutter the page if you overuse them.

Tips for Better PDF Comments

A few things I've learned from doing a lot of document reviews:

Be specific. "This doesn't work" is not helpful feedback. "This figure shows Q3 data but the text references Q4 — which is correct?" gives the person something to act on.

Use the right tool for the job. Don't put a sticky note on a paragraph when a text highlight with a comment would make your point clearer. Don't draw a rectangle around text when you could just highlight it.

Keep it professional. Comments in a PDF might get forwarded to people you don't expect. Write as if the CEO might read your notes. (I've seen this go wrong.)

Consolidate your comments. If you have three thoughts about the same paragraph, put them in one note. Nobody wants to click through fifteen icons on a single page.

Flatten when you're done. If you're sending a final version after incorporating feedback, flatten the PDF to remove all the comment layers. OnlyDocs can do this in one click. You don't want old review notes showing up in the finished document.

Can You Add Comments on Mobile?

Yes, but the experience varies. On iOS, the built-in Files app and Books app both support basic PDF markup. Android doesn't have great native options, so you'll want a third-party app like Xodo or the Adobe Reader mobile app.

For quick "I need to add one note on my phone" situations, mobile works fine. For actual review work, sit down at a computer. Your thumbs will thank you.

Wrapping Up

Adding comments and sticky notes to a PDF is one of those things that seems like it should be obvious — and with the right tool, it is. You don't need expensive software. You don't need to convert the PDF to Word and back. Just open it, click where you want to comment, and type.

If you want the quickest path, OnlyDocs handles it right in your browser with no signup. For heavier annotation work, Adobe Reader is free and full-featured. And if you're on a Mac, Preview is already sitting right there.

The real trick isn't the tool — it's leaving comments that are actually useful. Be specific, be clear, and put your notes exactly where they belong. Your collaborators will appreciate it.