How to Add Comments to PDF: Complete Guide Collaborating on PDF documents often requires leaving feedback, asking questions, or highlighting important sections. Adding comments to PDFs allows reviewers, editors, and team members to communicate without altering the original content. This guide covers every method to add comments to PDFs: using online tools (fastest, collaboration‑friendly), Adobe Acrobat Pro (professional), free desktop software (PDF‑XChange Editor), and built‑in viewers (Preview on Mac, Edge on Windows). You will learn how to add sticky notes, highlight text, underline, cross out, draw shapes, add text boxes, and even reply to comments. By the end, you will be able to use PDF annotations effectively for proofreading, peer review, and document collaboration. Why Add Comments to a PDF? Feedback and review: Mark up contracts, reports, or student assignments without changing the original text. Questions and clarifications: Insert sticky notes to ask the author about specific sections. Highlight important information: Draw attention to key points using highlighter tools. Track changes: Use strikethrough and underlines to suggest edits. Collaborative work: Multiple reviewers can add comments, and authors can resolve them. Types of PDF Comments (Annotations) Comment Type Description When to Use Supported By Sticky Note A yellow note icon that opens a text box for comments. Does not cover content. General feedback, questions, suggestions. All tools Highlight Colored background overlay on selected text. Emphasizing important phrases, marking errors. All tools Underline / Strikethrough Lines under text or through text. Suggested additions (underline) or deletions (strikethrough). Acrobat, PDF‑XChange, online tools Text Box Free‑floating rectangle with typed text. Adding explanatory text that stays on the page. Acrobat, PDF‑XChange, some online Draw / Freehand Draw arrows, circles, or freeform lines. Pointing to specific elements, diagram markup. Acrobat, PDF‑XChange Stamp Predefined or custom stamps (e.g., "Approved", "Confidential"). Status indicators, approval workflows. Acrobat Pro Method 1: Add Comments Online (Fastest, No Installation) Online PDF editors are ideal for quick annotation of non‑sensitive PDFs. Avoid uploading confidential documents. Using Our Edit PDF Online Tool: Go to Edit PDF Online. Upload your PDF. Click the Comment or Annotate button in the toolbar (speech bubble icon). To add a sticky note: Click on the page where you want the note. Type your comment. To highlight text: Select the text, then click the highlighter icon. Choose color (yellow, green, pink, etc.). To add a text box: Click the "Text" tool, draw a box, and type. To draw shapes: Use the shape tools (rectangle, circle, arrow, line). All comments are saved with the PDF. Click "Download" to get the annotated PDF. Your file is processed in your browser and never uploaded to our servers. Alternative Free Online Annotation Tools: Sejda Annotate PDF: 50 MB limit, 200 pages, 3 tasks/hour. Supports highlights, notes, text boxes, shapes. SmallPDF Add Comments: Free tier with daily limits, basic sticky notes and highlights. PDFescape (online): 10 MB, 100 pages – offers sticky notes, highlights, and drawing. Xodo (online version): Free, no registration, supports full annotation suite. Privacy warning: Do not upload sensitive PDFs to any online tool. Use offline software for confidential files. Method 2: Add Comments Using Adobe Acrobat Pro Adobe Acrobat Pro provides the most comprehensive comment and review tools, including collaboration features. Open the PDF in Adobe Acrobat Pro. Click the Comment tool in the right panel (speech bubble icon). The comment toolbar appears at the top. Options include: Sticky Note: Click on the page and type your comment. Highlight: Select text, then click the highlighter button. Underline / Strikethrough: Select text, choose from markup dropdown. Add Text Box: Click the "T" icon, drag a box, type. Draw Freehand: Use the drawing pencil and shape tools. Stamp: Choose from standard stamps (Approved, Confidential, etc.) or create custom stamps. Comments appear in the right sidebar. You can reply to comments, mark them as resolved, or delete them. To review comments from multiple users, use the Share for Review feature (cloud‑based collaboration). Save the annotated PDF (File > Save As). Method 3: Add Comments Using Free Desktop Software (Offline, Private) These tools work offline and keep your files private. Some add watermarks, but annotation works. PDF‑XChange Editor (Free version, Windows): Open the PDF in PDF‑XChange Editor. Use the Comment and Markup tools from the toolbar: Sticky Note: Click the note icon, then click on the page. Highlight: Select text, click the highlighter icon. Text Box: Click the "T" in a box icon, draw, type. Drawing: Use the Callout, Arrow, Rectangle, Oval, or Pencil tools. Comments appear in the Comments panel (left sidebar). You can edit, delete, or export comments. Save the PDF. The free version adds a small watermark, but all annotations remain. Preview (Built‑in on Mac, Free): Open the PDF in Preview. Click the Markup toolbar button (looks like a pencil tip inside a circle). Tools available: Text Selection: Highlight text. Sticky Note: Click the note icon, then click on the page. Type your comment. Text Box: Insert a text box and type. Shapes: Add arrows, lines, rectangles, circles, speech bubbles. Signature: Add a signature (for signed approvals). Save the PDF (File > Save). Preview does not have a comment sidebar, but sticky notes are visible. Microsoft Edge (Built‑in, Windows): Open the PDF in Microsoft Edge browser. Click the Add notes button (pen icon) in the top toolbar. Tools available: Pen, Highlighter, Eraser, Add sticky note, Text box, Add text, Draw shape. After annotation, click Save (disk icon). Comparison Table: PDF Commenting Methods Method Price Sticky Notes Highlight Text Box Draw Shapes Reply to Comments Privacy Online Editor (DonePDF) Free ✅ Yes ✅ Yes ✅ Yes ✅ Yes (basic) ❌ No Files uploaded Adobe Acrobat Pro ~$15/month ✅ Yes ✅ Yes ✅ Yes ✅ Yes (advanced) ✅ Yes (share for review) Local (or cloud) PDF‑XChange Editor (free) Free (watermark) ✅ Yes ✅ Yes ✅ Yes ✅ Yes ✅ Yes (comments panel) Local Preview (Mac) Free ✅ Yes ✅ Yes ✅ Yes ✅ Yes (limited) ❌ No Local Microsoft Edge (built‑in) Free ✅ Yes ✅ Yes ✅ Yes ✅ Yes (pen, shapes) ❌ No Local Step‑by‑Step Workflow: Collaborative PDF Review Share the PDF with your team (via email or cloud). Each reviewer opens the PDF in Adobe Acrobat Pro, PDF‑XChange Editor, or online tool. Reviewers add comments: Use sticky notes for questions or general feedback. Use highlight for important sections. Use underline for suggested additions, strikethrough for deletions. Use drawing tools to point to specific areas. If using Adobe Acrobat Pro with "Share for Review", comments sync to the cloud; multiple reviewers can see each other's comments. The author compiles all feedback, answers comments, or marks them as resolved. Export comments summary (Acrobat Pro can export comments to a Word or PDF report). Best Practices for Adding Comments to PDFs Be specific: Place sticky notes directly next to the relevant text. Use color coding: Use different highlighter colors for different types of feedback (e.g., yellow for suggestion, green for approval, pink for error). Keep comments concise: Long paragraphs in sticky notes are hard to read; split them into multiple notes. Use text boxes for longer explanations: Text boxes can contain multiple lines and are visible without clicking. Reply, don't delete: In collaborative workflows, use the reply feature (Acrobat Pro or PDF‑XChange) to maintain a conversation thread. Flatten annotations for final distribution: If you want comments to become permanent and not editable, flatten the PDF (print to PDF). Common Mistakes When Adding Comments to PDFs Using browser viewer that does not save comments: Browsers like Chrome have a "Preview" mode that does not save annotations. Always use a dedicated tool or the Edge browser (which supports saving). Not saving after adding comments: In online tools, you must click "Download". In desktop software, Save (Ctrl+S). Placing sticky notes over text: Move the note icon to the margin so the original text remains visible. Forgetting to flatten before sending final version: Recipients may accidentally move or delete comments. Flattening turns comments into static content. Uploading sensitive PDFs to unknown online annotators. Use offline tools for confidential documents. Tools for PDF Management – DonePDF Utilities Edit PDF Online – Add sticky notes, highlights, text boxes, and shapes Sign PDF – Add signature as a comment (for approvals) Compress PDF – Reduce file size after adding many comments (compression does not remove comments) Protect PDF – Prevent others from editing or deleting your comments Merge PDF – Combine commented PDFs from multiple reviewers You May Also Like – Related Articles How to Highlight Text in PDF How to Edit a PDF File How to Add Digital Signature to PDF How to Remove Sensitive Data from PDF Related PDF Tutorials – Complete Learning Path Introduction & Basics What is a PDF File History of PDF Format Editing & Annotation How to Add Comments to PDF How to Highlight Text in PDF How to Edit a PDF File How to Add Text to PDF How to Add Image to PDF Page Management How to Organize PDF Pages How to Split PDF Files How to Merge PDF Files Security & Signatures How to Protect PDF from Editing How to Verify PDF Signature Use Cases Best PDF Tools for Business How to Use PDF for Contracts Common PDF Problems and Solutions Conclusion – Add Comments to PDFs Like a Pro Adding comments to PDFs is essential for collaboration, proofreading, and document review. For quick, non‑sensitive files, use our free online Edit PDF Online tool (sticky notes, highlights, text boxes). For professional team reviews with reply and resolution tracking, use Adobe Acrobat Pro. For offline, private annotation on Windows, PDF‑XChange Editor is excellent. Always save your work, use color coding, and flatten the final version before distribution. With the methods and best practices in this guide, you can effectively communicate feedback on any PDF document. Frequently Asked Questions How can I add comments to a PDF for free? You can add comments to a PDF for free using these methods: Online (fastest): Use our Edit PDF Online tool. Upload, use sticky notes, highlight, text boxes, shapes. Download the annotated PDF. No registration, auto‑deletion. Offline (Windows): PDF‑XChange Editor (free version) – open PDF, use comment tools (sticky notes, highlight, text box, drawing). Saves with watermark. Offline (Mac): Preview (built‑in) – open PDF, click Markup toolbar, add sticky notes, highlights, shapes, text boxes. Offline (Windows Edge): Edge browser – open PDF, click "Add notes", use pen, highlighter, sticky notes, text. For sensitive documents, use offline tools. For quick, non‑confidential files, our online tool is fastest. How do I add a sticky note comment to a PDF? To add a sticky note (annotation) to a PDF: Our online tool: Open Edit PDF Online, upload PDF, click the comment/sticky note icon, click on the page where you want the note, type your message, save/download. Adobe Acrobat Pro: Open PDF, click Comment icon (right panel), select Sticky Note tool, click on page, type comment. Save. PDF‑XChange Editor: Click the Sticky Note icon (yellow note) in the toolbar, click on page, type, save. Preview (Mac): Open PDF, click Markup toolbar (pencil), select the note icon, click on page, type, save. Sticky notes appear as a small icon; readers can click to see the full comment. They are ideal for questions or general feedback. How do I highlight text in a PDF? To highlight text in a PDF document: Our online tool: Upload to Edit PDF Online, select the text you want to highlight, click the highlighter icon (choose color yellow, green, pink, etc.), download. Adobe Acrobat Reader (free): Open PDF, select the Highlight tool (or right‑click selected text > Highlight), choose color. PDF‑XChange Editor: Select text, click the Highlight button in the toolbar (or right‑click > Highlight). Preview (Mac): Select text, click the Highlight button (or right‑click > Highlight). Microsoft Edge: Open PDF, click "Add notes", select the highlighter tool, drag over text. Highlights are useful for marking important sections, errors, or places that need review. How do I add a text box to a PDF? To add a free‑floating text box (for additional comments or instructions): Our online tool: Upload to Edit PDF Online, click the "Text" tool (T icon), drag a rectangle on the page, type your text, adjust font and size, download. Adobe Acrobat Pro: Open PDF, click Comment > Add Text Box, draw a box, type. (Note: Acrobat Reader free version does not support adding text boxes; use Pro or online.) PDF‑XChange Editor: Click the "Text Box" tool (T in a box), draw rectangle, type, adjust properties. Preview (Mac): In Markup toolbar, click the "Text Box" tool (T in a box), drag, type. Text boxes are visible on the page without needing to click; they are good for longer instructions. Can I draw or add shapes to a PDF as comments? Yes, drawing tools allow you to add arrows, lines, rectangles, circles, and freehand drawings: Our online tool: In Edit PDF Online, use the shape tools (line, arrow, rectangle, circle) in the toolbar. You can also draw freehand with the pen tool. Adobe Acrobat Pro: Comment > Drawing tools: Arrow, Line, Rectangle, Oval, Polygon, Cloud. Use the pencil for freehand. PDF‑XChange Editor: Callout, Arrow, Rectangle, Oval, Pencil, Line tools available in the Comment toolbar. Preview (Mac): Shapes: Line, Arrow, Rectangle, Oval, Speech Bubble (limited). Shapes are useful for pointing to specific elements, circling errors, or adding visual emphasis. How do I reply to comments in a PDF? Replying to comments allows threaded discussions within the document: Adobe Acrobat Pro: In the Comments panel (right sidebar), right‑click a comment and select "Reply" or click the reply icon (curved arrow). Type your response. This creates a nested thread. Requires Acrobat Pro (not free Reader). PDF‑XChange Editor: In the Comments panel, select a comment, click "Reply" (or right‑click > Reply). The free version supports replies. Online tools: Most free online commenters (including our Edit PDF Online) do not support threaded replies. For collaborative review with multiple users, use Acrobat Pro with "Share for Review" (cloud‑based). Replying is essential when multiple reviewers collaborate on the same PDF. Can I add comments to a PDF on my phone? Yes, you can add comments to PDFs on mobile devices: Adobe Acrobat Reader (free, iOS/Android): Open PDF, tap the comment bubble icon (or markup icon). You can add sticky notes, highlights, underlines, strikethroughs, and draw freehand. Free version does not support text boxes or shape tools. Xodo PDF (free, iOS/Android): Full annotation suite: sticky notes, highlights, underlines, text boxes, shapes, freehand drawing. Excellent for commenting. Our online tool via mobile browser: Edit PDF Online works on any smartphone browser – upload, add comments, download. Less convenient but no app needed. Mobile annotation is great for on‑the‑go review, but for heavy collaboration, use a desktop. How do I remove comments from a PDF? To delete comments (sticky notes, highlights, text boxes, drawings): Adobe Acrobat Reader (free) or Pro: Right‑click on the comment (sticky note icon, highlighted text, shape) and select "Delete". To delete all comments, go to Comment panel > Options > Delete All Comments. PDF‑XChange Editor: Right‑click comment > Delete. Delete multiple by selecting in Comments panel and pressing Delete. Our online tool: Upload the PDF, select the comment, click the trash icon, download. Preview (Mac): Select the comment annotation and press Delete. If the PDF is flattened (printed to PDF), comments become permanent and cannot be removed. Keep a copy of the annotated original if you might need to change comments later. What is the difference between a sticky note and a text box? Sticky note: A small yellow note icon placed on the page. The comment text is hidden until the user clicks the icon. It does not cover the underlying content. Sticky notes are ideal for questions, suggestions, or general feedback where you do not want to obscure the original text. Text box: A free‑floating rectangular box that contains visible text. The text is always visible on the page. It can be moved and resized. Text boxes are better for longer instructions, labels, or explanations that need to be seen immediately without clicking. Both are useful in different scenarios. Use sticky notes for unobtrusive comments, and text boxes for visible annotations.