[Top 17 Tools] How to Add Comments in PDF in Easy Steps

PDF comments (also called annotations/markups) let users add feedback, edits, highlights, notes, and collaborative feedback without rewriting original document content. Every industry relies on PDF commenting: students marking textbooks, writers editing manuscripts, lawyers reviewing contracts, designers checking layouts, and enterprise teams sharing document feedback remotely.

This guide breaks down every annotation format, ranks 17 trusted tools, compares critical buying factors, and names the #1 online and desktop PDF comment solution for all user cases.

How Can I Add Comments in PDF? Online or Desktop?

The decision between online and desktop tools comes down to three core factors: privacy, frequency, and complexity. Check the chart below and choose a suitable solution for adding comments in PDF.

Now that you know which type of tool to choose based on your situation, here are 10 recommended desktop applications and 7 online tools—let's take a look at the differences between them.

Top 10 Tools to Add Comments in PDF (Free & Paid Offline Software)

Covers Windows/Mac support, pricing, full comment feature set, collaboration, watermark rules; #1 Top Desktop Pick: UPDF！

UPDF balances affordable pricing, cross-platform support, complete professional comment feature set, full offline privacy, and zero export watermarks. It covers casual personal users, student research, small business contract review, and lightweight enterprise team collaboration — outperforming expensive Adobe Acrobat while being more feature-rich than limited free desktop alternatives.

Add PDF Comments in UPDF (Best Desktop All-Rounder)

1. Download & install UPDF for Windows/Mac/iOS, launch the software and open the PDF
2. Navigate to the top menu bar and click the Comment tab to open the full annotation toolkit
3. Pick any comment type: freehand pen, measurement markup, file attachment, redaction, custom stamp
4. Customize comment color, font size, transparency via style panel
5. Manage all comments in the right sidebar: filter by status, batch export all feedback to Excel
6. Save annotated PDF locally or sync to cloud for team shared review

UPDF also allows you to compare the pages before and after comments. Go to the toolbar and choose Compare. Then you can clearly see the changes.

What's more, you can export all comments as Text or PDF, then you can see all highlighted or underlined text.

Text comments are the most fundamental form of communication in PDF collaboration, supporting threaded replies and status management. Refer back to How to Annotate PDF to view the collaborative workflow for comments and sticky notes.

Top 7 Free Online Tools to Add Comments in PDF

Each tool includes key free limits, supported comment types, and watermark rules. #1 Top Online Pick: Adobe Acrobat Online Reader.

Adobe Reader solves the top 3 user pain points of free online tools: no mandatory export watermarks, full cross-PDF compatibility for editable comments, trusted secure cloud storage, and complete basic annotation types without overly strict file quotas. Perfect for casual, cross-device PDF commenting for non-confidential work.

Add PDF Comments in Adobe Acrobat Online Reader (Best Online)

1. Open Adobe Acrobat Online in any browser, upload your target PDF file
2. Locate the Comment toolbar on the right sidebar
3. Select desired comment type: Sticky Note, Highlight, Callout, Stamp, Shapes
4. Click anywhere on the PDF page to place markup, type your feedback text
5. Use the reply icon under existing comments to start team discussion threads
6. Click Download → Export PDF; no watermark saved to local device

Full List of PDF Comment Types You Need to Know

Professional PDF tool - UPDF supports these comment categories; free lightweight online tools often cut advanced markup types. We split into 7 core comment groups. You can download UPDF now and try these features one by one!

1. Text Pop-Up Comments (Text Notes)

1. Sticky Note / Pop-up Note: Floating yellow memo, click to expand text, no permanent on-page text
2. Text Box: Fixed visible text block on PDF page, permanently displayed
3. Free Text / Typewriter: Direct typing over PDF content without border boxes
4. Callout Comment: Text box + directional arrow for labeling charts, diagrams, small text sections

2. Text Markup Comments (Mark Original PDF Text)

1. Highlight: Colored background for key sentences
2. Underline: Straight line under important text
3. Squiggly Underline: Mark typos, grammar errors, questionable content
4. Strikethrough: Cross out text to mark deletions
5. Replace Text: Strikethrough original text + insert replacement copy for editing drafts

3. Drawing & Shape Markup Comments

• Rectangle, Oval/Circle, Polygon, Cloud shape frames to highlight blocks
• Straight Line, Arrow for pointing elements
• Freehand Pencil/Pen: Digital handwriting, sketch markup, handwritten feedback

4. Stamp Comment

Pre-built official stamps: Approved, Draft, Confidential, Sign Here, Rejected; custom image stamps (logos, hand signatures)

5. Attachment Comments

1. File Attachment: Embed Word, Excel, images, ZIP files as comment attachments
2. Audio Voice Note: Record audio feedback attached to PDF sections (advanced feature)

6. Professional Specialized Comments

1. Measurement Markup: Distance, area, perimeter labels for engineering/architecture PDF drawings
2. Redact Comment: Permanent blackout to hide sensitive confidential data
3. Signature / Initial Comment: Quick signature markups for document approval

7. Collaborative Comment Functions

• Reply Threads: Respond to single existing comments for team discussion
• Comment Status Tags: Accepted / Rejected / Completed / For Review
• Batch Export Comments: Extract all feedback into CSV/TXT report for audit

FAQS About Adding Comments in PDF

Q1. How to Add Comments to a PDF in Google Drive?

If you already have a PDF in Google Drive, you can click the "Three Dots" after the PDF document, select "Open With" > "Preview", click "Add a comment", and highlight the content to add a comment.

Q2. How to Add Comments in PDF with Adobe Reader?

You can open the PDF file with Adobe Reader, now, click the "Add a Comment" icon at the left side menu, click the place where to add the comments, enter the content, and then, save it.

Q3. How to Add Comments to PDF in Preview?

Open the PDF in preview, and click "Show Markup Toolbar" > “Note” to type the text comments in the PDF with preview.

Conclusion

Many people don't know how to add comments in PDF files, which may prevent them from smart learning and collaboration. With this article, we are sure that you know how to add comments in PDF now. Whether you need to add comments to PDF on a computer or on a mobile device, you can use UPDF. Why not download UPDF via the button to try it now? And if you like this tool after testing, you can upgrade to the pro version at a low price.