How to Collaborate on PDFs: Review, Comment, and Track Changes

The Challenge of Collaborating on PDFs

PDFs are designed to be fixed — that's their strength for distribution, and their frustration for collaboration. Unlike Word documents with real-time co-editing, PDFs require specific workflows to gather feedback, track changes, and consolidate multiple reviewers' comments.

But done right, PDF collaboration is efficient and professional, especially for documents that must maintain precise formatting through review cycles.

Annotation Tools: What They Do

Before choosing a platform, understand what PDF annotation tools exist:

Sticky Note Comments

The most common annotation. Adds a coloured pin to the page; clicking it reveals the comment text. Ideal for general feedback, questions, or suggestions tied to a specific location.

Text Highlights

Select text and highlight it (yellow, green, blue, etc.). Often used with an attached comment explaining why that text is highlighted.

Strikethrough and Underline

Mark text for deletion (strikethrough) or emphasis (underline) with an optional comment.

Text Insertion Markers

A caret symbol (^) indicates where new text should be inserted. Used in proofreading workflows.

Drawing Tools

Free-hand drawing, circles, rectangles, and arrows to mark up visual content — diagrams, charts, layouts.

Text Boxes

Add visible text directly on the page surface — useful for instructions, labels, or corrections that should be immediately visible without clicking.

Stamps

Pre-made or custom images like "APPROVED", "DRAFT", "CONFIDENTIAL", or "REVIEWED" that can be applied to pages.

Free Tools for PDF Collaboration

Adobe Acrobat Reader (Free)

The most widely used PDF viewer includes solid annotation tools:

• Sticky notes
• Highlighting
• Drawing tools
• Strikethrough and underline

Shared Review: Adobe offers a free "Send for Comments" feature through the free Reader app (requires an Adobe account). Recipients annotate in Reader; comments are stored and visible to all reviewers.

PDF.js (Browser-Based)

Firefox uses PDF.js to display PDFs in-browser. Limited annotation support.

Xodo PDF (Free, Mobile and Desktop)

Full-featured annotation tools on iOS, Android, Windows, and web. Supports real-time collaboration via cloud-synced documents.

Foxit PDF Reader (Free)

Includes commenting, annotations, form filling, and a cloud review feature (Foxit Connected PDF).

Professional Tools for PDF Collaboration

Adobe Acrobat Pro

The industry standard for PDF collaboration with the most complete feature set:

• Send for Review: Email-based review workflow; comments are emailed back and merged
• Shared Review: All reviewers see each other's comments in real time via cloud storage
• Comment & Markup panel: Lists all annotations with status (accepted/rejected), author, date
• Compare Documents: Highlights differences between two versions of a PDF

Shared Review setup:

1. Tools → Comment → Send for Comments
2. Choose email or shared drive
3. Recipients annotate and submit; all comments visible to everyone

Foxit PDF Editor (Paid)

Strong enterprise collaboration features with a lower price point than Acrobat. Supports DocuSign integration and shared review.

Nitro PDF Pro

User-friendly alternative with email review and comment consolidation.

Cloud-Based PDF Collaboration Platforms

Adobe Document Cloud

Tightly integrated with Acrobat Reader. Shared review via Document Cloud means all reviewers see comments in real time, across devices.

Google Drive

Surprisingly effective for PDF review. Upload a PDF → open with Google Docs for basic comments. Collaborators can use Google Docs commenting features (though layout may shift for complex PDFs).

For native PDF annotation in Google Drive, install Kami or Xodo as a Drive add-on.

Kami (Google Workspace / Education)

Popular in education and professional contexts. Browser-based, integrates with Google Drive, Classroom, and Canvas. Supports highlighting, text boxes, audio comments, and real-time collaboration.

Box and Dropbox

Both support basic PDF preview and annotation directly in the browser, making them useful for quick team review without additional software.

Workflow: Multi-Reviewer PDF Review

When you have several reviewers, structure the workflow to avoid chaos:

Step 1: Prepare the PDF for Review

• Lock the document structure (prevent page additions/deletions) if needed
• Add a "Review Version" stamp
• Name the file clearly: Proposal_v2_FOR_REVIEW_2024-03-15.pdf

Step 2: Send to Reviewers with Instructions

Don't assume reviewers know how to annotate. Include brief instructions:

• Which tools to use (highlight + comment for text changes; sticky notes for general feedback)
• What deadline to meet
• Where to return the annotated file

Step 3: Collect and Consolidate Comments

In Acrobat Pro: Comments → Import Comments from file (for emailed-back PDFs)

This merges comments from multiple annotated copies into a single PDF, showing each reviewer's name and colour.

Step 4: Review and Resolve

Work through each comment:

• Mark as "Accepted" or "Rejected"
• Apply changes to the source document
• Reply to questions

Step 5: Distribute the Final Version

Export a clean final PDF (no annotations) for distribution. If the review record needs preserving, create a separate "Review Archive" copy with all comments intact.

Tracking Changes vs. Comments

PDF doesn't have "Track Changes" the way Word does — there's no built-in mechanism to see deleted and added text marked up in the document itself.

Workarounds:

1. Comment + Strikethrough: Use strikethrough to mark deleted text and a sticky note with the replacement text. This mimics Track Changes visually.

2. Compare Documents (Acrobat Pro): After a revision, compare the original and revised PDFs. Acrobat highlights all changes between versions — text additions, deletions, and formatting changes. Access via Tools → Compare Files.

3. Edit in the source and export: Many teams prefer to make changes in Word/InDesign and export a new PDF version, using Acrobat's Compare Documents to verify what changed.

Digital Signatures in Review Workflows

For documents requiring approval, combine review with digital signatures:

1. Reviewers annotate the PDF
2. All comments are resolved
3. Approver applies a digital signature certifying the document is complete and approved
4. A certified/signed PDF cannot be modified without invalidating the signature — providing audit evidence

Mobile PDF Collaboration

For on-the-go review, mobile annotation apps work well:

• Adobe Acrobat (iOS/Android): Full annotation sync via Adobe cloud
• Xodo: Free, powerful, syncs via Dropbox/Google Drive/OneDrive
• GoodNotes / Notability (iPad): Popular for handwriting annotations with Apple Pencil
• Microsoft Edge (Android): Built-in PDF annotation for quick markup

Best Practices for PDF Collaboration

1. Version control: Use clear version numbers (v1, v2, Final, Final_Approved) in filenames
2. One PDF per round: Avoid sending multiple PDFs for the same review round — consolidate
3. Set comment deadlines: Without a deadline, reviews drag on
4. Use reviewer colours: In Acrobat, each reviewer gets a unique colour — this makes scanning for specific feedback easier
5. Don't send editable source files unless necessary — PDF keeps layout fixed during review
6. Archive annotated versions: Keep the annotated PDFs as a record of the review process

Summary

PDF collaboration works best with the right tool and a clear workflow. For individual or small-team reviews, free tools like Adobe Acrobat Reader or Xodo are sufficient. For enterprise workflows with multiple reviewers and approval chains, Acrobat Pro's Shared Review or cloud platforms like Kami provide the structure needed to manage the process efficiently. The key is establishing a consistent workflow — version control, clear instructions, and comment consolidation — rather than letting review PDFs multiply into chaos.