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Annotate PDFs on Windows, Mac, and Mobile: When Structured Notes Help

Updated · 11 min read

Annotate PDFs on Windows, Mac, and Mobile: When Structured Notes Help

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To annotate a PDF right now, open it in a viewer with markup tools, add highlights, notes, or drawings, and save a working copy before you share it. Use your device's built-in tool, Preview on Mac or Chrome in a browser, for quick marks. Reach for a collaboration-capable platform when you need threaded review, synced comments, or citation-aware research notes.

TL;DR:

  • Annotating a PDF using built-in tools like Preview on Mac or Chrome supports highlights, notes, and drawings, but does not allow editing of existing text.
  • On Windows, Chrome's built-in PDF viewer enables drawing, highlighting, and signatures directly in the browser without additional software.
  • Cloud storage platforms such as Google Drive facilitate commenting and threaded discussions, though comments might not transfer to all PDF readers.
  • Mobile devices support touch input and signatures, with tools like Acrobat Reader offering offline markup and team review features.
  • For long-term research, structured platforms like Omphalis attach notes directly to original passages and keep annotations searchable and organized over time.

Table of Contents

What tools can you use to annotate a PDF?

Most people already own a capable annotation tool. Built-in viewers like Apple's Preview and the Chrome PDF viewer handle highlights, notes, and drawings with no download. Cloud storage tools such as Google Drive add commenting on top of a shared file. Mobile apps extend the same markup tools to touch and pencil input. Specialized platforms built for research, including Omphalis, keep annotations attached to structured notes instead of loose comments. Developers can also build annotation directly into a product using an embed API.

The tools support several annotation types:

  • Highlights, underlines, and strikethroughs for marking passages.
  • Text boxes and sticky notes for written comments.
  • Shapes, stamps, and freehand ink for drawn feedback or signatures.

A viewer lets you mark up a document without touching its underlying text, while a full editor changes the text itself. This distinction is worth knowing before you pick a tool for a quick comment versus a correction.

How do you annotate a PDF on Windows?

Windows users can annotate without installing anything extra, using Chrome's built-in PDF viewer, which supports drawing, highlighting, and signature tools directly in the browser.

  1. Open the PDF in Chrome, which loads it in its built-in viewer.
  2. Select Draw from the toolbar.
  3. Choose Pen or Highlighter, then set your color and size.
  4. Add your marks, using Eraser, Undo, or Redo as needed.
  5. Click Save or Export to keep a working copy.

To add a signature, use the same Draw tool and sign with your mouse or trackpad before saving. A normal save keeps most annotations editable, while printing to PDF typically flattens them into the page. If you need to change text that already exists in the document, rather than mark it up, you need a full PDF editor instead of a viewer.

Pro Tip: Save a fresh copy before you start marking up anything you might need unannotated later.

How do you annotate a PDF on Mac using Preview?

Preview, built into every Mac, handles most everyday markup needs through its Markup toolbar, as Apple's own guidance describes.

  • Open the PDF in Preview and click the Markup toolbar icon to reveal the tools.
  • Use the highlighter, text, note, or signature tool, then drag to place, move, or resize each annotation.
  • Choose File > Save or File > Export to keep annotations editable for later changes.
  • Choose Print > Save as PDF only when you want to lock annotations permanently into the page.

Preview marks up a document well, but it cannot edit text that already exists in the PDF. For that, you need a different tool entirely. The save method you choose determines whether a colleague can still adjust your comments after you send the file, so pick deliberately based on whether the document is still in draft.

How do you annotate a PDF in a browser or in Google Drive?

Browser-based annotation works well for quick marks you do not need to keep syncing across a team. In Chrome, open the PDF in a new tab, select Draw, pick Pen or Highlighter, set your color and size, mark up the page, and click Done to save.

Google Drive adds a comment layer on top of an uploaded file, according to the University of Wisconsin Whitewater's annotation guide:

  • Upload the PDF to Drive and open it.
  • Highlight the text you want to discuss and select Add comment.
  • Share the file with collaborators who have commenting permission, and replies thread under the original comment.

Comments added in Google Drive do not always carry over into every standalone PDF reader, according to the same guide, so test a shared file with your actual recipients before relying on it for a formal review.

How do you annotate PDFs on a tablet or phone?

Touch devices make freehand markup and signatures faster than a mouse ever could.

  • On an iPad, import the PDF into Files or a markup-capable app, then use Apple Pencil or the Markup tool for highlights, written notes, and signatures, exporting the result when you finish.
  • On Android, Acrobat Reader's shared-review features support comments, threaded replies, and offline markup that syncs once you reconnect.
  • Reviewer names and colors in Acrobat Reader help a team track who commented on what during a shared review.

Sign documents directly with a finger or stylus rather than typing a name, and test your sync by closing and reopening the file before you consider a review finished. Offline edits should always sync once you are back online, but confirming it once saves a headache later.

How do shared PDF reviews and annotation exchange actually work?

Teams reviewing the same document generally choose between two models. Annotations can live embedded inside the PDF itself, traveling with the file wherever it goes, or they can be stored separately as XFDF or FDF files and merged in later. The PDF Association's guidance on combining XFDF files notes that this exchange format is standardized and widely used for controlled reviews, though merging annotation files back into a PDF requires the files to match and sometimes needs manual adjustment if the source document changed in the meantime.

To manage a shared review without losing comments:

  1. Invite reviewers and confirm which PDF version they are marking up.
  2. Track replies and resolved comments as they come in, rather than waiting until the end.
  3. Export a comment list periodically so you have a record outside the live file.
  4. Keep the original, unannotated PDF untouched as a reference copy.

Pro Tip: Before merging XFDF annotations into a final document, test the merge on a copy first, since mismatched files can drop or misplace comments.

How do you make PDF annotations accessible?

Visible marks alone do not make an annotation usable for everyone. According to W3C's PDF accessibility techniques, accessible annotation depends on tagged PDF structure and Unicode-mapped text so that assistive technology can find and read the content, not just display it.

  • Write descriptive comments instead of relying on a highlight color alone to convey meaning.
  • Keep annotation text mapped to Unicode and tied to the correct structure element in a tagged PDF.
  • Maintain adequate contrast between annotation marks and the page background.

A tagged, Unicode-mapped PDF structure lets screen readers access annotation text and determine reading order, per the W3C's techniques for accessible PDFs, something a purely visual highlight cannot do on its own. Before sending a document out, test it with a screen reader and confirm your export preserves tags rather than flattening the structure away.

When does a structured annotation platform like Omphalis make sense?

In-file markup works well for quick feedback, but it starts to strain once you are managing dozens of papers or articles over months of research. Some platforms are built differently: instead of loose comments scattered across files, they attach your notes directly to the original passage, explain difficult sections inline, and keep everything searchable later.

We support importing PDFs alongside EPUBs, Word documents, and feeds, so research from different formats lands in one place. Our browser extension lets you save an article or PDF the moment you find it, and our research paper tools are built specifically for readers working through dense academic material. You keep your original source intact while building a layer of structured notes and citations around it, which matters most once a project outlives a single markup session.

When does a structured annotation platform like Omphalis make sense? — overview diagram

When should you annotate instead of edit?

Annotation is the right tool for feedback, study notes, and review, since it leaves the source untouched while recording your thinking. The moment you need to change the actual wording of a document, you need a full editor, not a markup tool. Always save a working copy first, and check that your recipient's viewer displays your comments the way you expect before you call a review finished.

For research or teaching, pairing markup with structured notes keeps context and citations attached to the source long after the original review ends.

**

Try Omphalis for notes that stay attached to the source

Annotating a PDF solves the moment. Keeping those notes useful months later is a different problem that some platforms aim to solve by turning saved articles, papers, and PDFs into a structured reading space where notes sit next to the original passage, difficult sections get explained inline, and everything stays searchable when you need it again.

Omphalis

  • Install our browser extension to save a PDF or article the moment you find it.
  • Check our pricing page for Free, Pro, Premium, and Scholar plans, including monthly and annual rates.
  • Import your first PDF and see how structured notes compare to a plain markup pass.

Start with the free tier and import a document you are currently working through.

FAQ

How do you make annotations on a PDF document?

Open the file in a viewer with markup tools, such as Preview on Mac or Chrome's built-in viewer on any platform, then select a highlight, note, or drawing tool and apply it to the page. Save or export the file afterward to keep a working copy, as described in Adobe's annotation guidance.

What is the best PDF annotator for Mac?

Preview, built into every Mac, covers most everyday needs through its Markup toolbar, which includes highlight, text, note, and signature tools according to Apple's support documentation. For ongoing research where you want notes to stay attached to specific passages across many documents, a structured platform like Omphalis adds organization that a simple viewer does not.

How do you annotate text effectively?

Effective annotation goes beyond highlighting: add descriptive comments that explain why a passage matters, not just color marking it, since annotation includes added text and graphics that convey interpretation, per the PDF Association's how-to guide. Keep notes specific enough that they make sense without the surrounding context months later.

What software can you use to annotate a PDF?

Built-in options like Chrome's PDF viewer and Apple's Preview cover quick highlights, notes, and drawings with no download required. For shared team reviews, Adobe's tools support programmatic annotation controls and comment panels through its PDF Embed API, while a platform like Omphalis fits better when you need notes organized across many sources over time.

Sources