How to Redline a PDF — Mark Up, Comment & Track Changes

If you've ever received a contract, legal document, or report as a PDF and needed to suggest edits, you know the pain. PDFs weren't designed for easy editing — they're meant to be final. But redlining a PDF (adding strikethroughs, comments, and markup) is absolutely possible, and you don't need expensive software to do it. This guide walks through every method worth using.

What Does "Redlining" a PDF Mean?

Redlining comes from the old-school practice of marking up printed documents with red pens. In the digital world, it means adding tracked changes — strikethrough deletions, insertions, comments, and annotations — so collaborators can see exactly what you want changed. It's standard practice in legal, academic, and corporate workflows.

The key difference between redlining a Word doc and a PDF: Word has native track changes built in. PDFs require annotation tools. But modern PDF editors have caught up, and the markup experience is nearly identical.

Method 1: Use a Free Online PDF Annotator

The fastest way to redline a PDF is right in your browser. No downloads, no accounts, no hassle. Online PDF annotation tools let you add comments, strikethrough text, highlight passages, and draw directly on the document.

How to do it:

• Open an online PDF annotator (like PeacefulPDF's editor)
• Upload your PDF — the file stays in your browser, nothing hits a server
• Select the text you want to mark up
• Choose your markup: strikethrough, highlight, underline, or add a comment
• For insertions, use the text comment tool to note what should replace the deleted text
• Download the annotated PDF when you're done

This approach is ideal for quick reviews. Everything runs client-side, so your documents stay private. The downside: you can't do true "track changes" with accept/reject flows online — that requires desktop software.

Method 2: Redline a PDF in Adobe Acrobat (Standard & Pro)

Adobe Acrobat is the gold standard for PDF markup, and for good reason. The annotation tools are robust, and if you're working with others who also use Acrobat, the commenting workflow is seamless.

Steps:

• Open the PDF in Adobe Acrobat
• Go to Tools > Comment to open the annotation toolbar
• Use the Strikethrough tool to mark text for deletion
• Use the Insert Text tool (caret marker) to suggest additions
• Right-click any markup and select Open Pop-up Note to add context
• Use Highlight or Underline for emphasis without deletion
• Save the annotated file or share it for review

Acrobat Pro also supports comparing two versions of a PDF side-by-side, automatically highlighting differences. If you're reviewing a revised contract against the original, this is a game-changer. Go to View > Compare Files and Acrobat will generate a redline report automatically.

The free Adobe Acrobat Reader includes most annotation tools — you don't need the paid version just to redline. Strikethrough, comments, and highlights are all available without a subscription.

Method 3: Redline a PDF on Mac with Preview

Mac users have a hidden gem built right into macOS: Preview. It's not just for viewing PDFs — it has solid markup tools that handle most redlining needs.

Steps:

• Open the PDF in Preview (it's the default viewer on Mac)
• Click the Markup Toolbar button (pen icon) or press Shift + Command + A
• Use the Strikethrough button (the "S" with a line through it) to mark deletions
• Add notes by clicking the Note button and typing your comment
• Use the Text tool to add insertion suggestions
• Save the file with your annotations

Preview's limitation: it doesn't support proper comment threading or reply-to-comment workflows. For solo markup it's great. For collaborative review rounds, you'll want something more powerful.

Method 4: Redline a PDF on Windows with Xodo

Xodo is a free PDF reader and editor for Windows that nails the annotation experience. It supports strikethrough, underline, highlight, text insertion, and comments — everything you need for redlining.

Steps:

• Download and install Xodo PDF Studio (or use the web version at xodo.com)
• Open your PDF and select the Annotate tab
• Highlight text and choose strikethrough, underline, or highlight
• Add comments by clicking the comment icon and typing
• Use the text box tool for longer insertion suggestions
• Export or save the annotated PDF

Xodo also syncs annotations across devices if you create a free account. Useful if you start redlining on your desktop and want to continue on your tablet.

Method 5: Convert to Word, Track Changes, Convert Back

Sometimes the best redline isn't a PDF redline at all. If you need a full track-changes workflow with accept/reject functionality, convert the PDF to Word first.

Steps:

• Convert the PDF to a Word document (.docx) using an online converter
• Open in Microsoft Word and enable Track Changes (Review tab)
• Make all your edits — deletions show as strikethrough, additions in color
• The recipient can accept or reject each change individually
• When the review is done, convert back to PDF

This method gives you the most powerful redlining experience, but it comes with a caveat: the PDF-to-Word conversion might mess up formatting, especially with complex layouts, tables, or unusual fonts. Always check the converted document before you start editing.

Best Practices for Redlining PDFs

Regardless of which tool you use, following these practices makes the review process smoother for everyone:

• Be specific in comments: "Change this to X" beats "fix this"
• Use consistent markup: strikethrough for deletions, insert comments for additions
• Number your comments if there are many — it makes discussion easier
• Save a copy of the original PDF before you start marking it up
• Flatten annotations before sending to someone who might accidentally edit them

Which Method Should You Use?

For quick, one-off redlines — use a free online annotator. It's fast, private, and handles 90% of what you need. For ongoing collaborative reviews with multiple reviewers, Adobe Acrobat or a dedicated tool like Xodo makes more sense. And if you need a true track-changes workflow with accept/reject, convert to Word first.

The tool doesn't matter as much as being clear and consistent in your markup. Pick what works for your situation and start redlining.