How to Annotate PDF for Free (Best Tools)
Learn how to annotate PDF for free using built-in tools and free desktop applications. Markup, highlight, and comment.
About This Tutorial
This guide was written and tested by Rachel Okafor, a Information Security & Compliance Consultant with 8 years of hands-on experience in document security, encryption, digital signatures, HIPAA compliance. Rachel has 8 years of experience in document security, previously serving as a compliance officer at a healthcare organization.
Annotating PDFs — highlighting, commenting, drawing, stamping — is possible with several free tools, but the capabilities vary dramatically. Microsoft Edge offers basic highlighting and drawing. macOS Preview adds text boxes and signatures. LibreOffice Draw provides shape tools but on an import-modify-reexport workflow. Understanding which free tool handles which annotation type saves significant trial and error.
This guide provides an honest comparison of four free PDF annotation tools, with no upselling. We tested each on the same set of documents and documented exactly where each tool succeeds and where it falls short.
Time to read: 5-7 minutes | Difficulty: Beginner to Intermediate | Last updated: 2026-07-21
Why This Matters
PDF annotations are a standardized feature set defined by the PDF specification (ISO 32000). The specification defines annotation types: highlight, underline, strikethrough, sticky note, text box, stamp, drawing, and attachment. However, not all PDF viewers implement all annotation types. Free viewers typically implement 3-5 types; desktop editors implement all types plus custom annotations.
A key limitation of free annotation tools: annotations are often not saved permanently to the PDF. Some viewers save annotations in a separate sidecar file rather than embedding them in the PDF. This means annotations may disappear when the PDF is opened in a different reader. Desktop editors always embed annotations in the PDF.
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Step-by-Step Using a Desktop PDF Editor
1 Choose the Right Free Tool for Your Annotation Type
For highlighting only: use Edge or Preview. For highlighting with comments: use Acrobat Reader (free). For text boxes and shapes: use Preview or LibreOffice Draw. For stamps: use Acrobat Reader. For drawing: use Edge, Preview, or LibreOffice Draw. Match the tool to the annotation type you need.
2 Open the PDF and Apply Annotations
Open the PDF in your chosen tool. Select the annotation type from the toolbar. For highlights: select text and click the highlight button. For comments: click the sticky note tool and click on the page. For shapes: select a shape and draw on the page. Save the file.
3 Verify Annotations Are Saved in the PDF
After saving, open the PDF in a different reader (not the one you used to annotate). Check that all annotations are visible. If annotations are missing, they were saved as sidecar data rather than embedded. Re-open in your annotation tool, and use 'Save As' to create a new copy — some tools embed annotations only with Save As, not Save.
4 Assess Whether Free Tools Met Your Needs
If the annotations display correctly across readers and you have all the annotation types you need, the free tool is sufficient. If annotations disappear in other readers, or you need annotation types the free tool does not support (custom stamps, callouts, flattening), consider a desktop editor.
5 For Professional Workflows: Consider a Desktop Editor
If you annotate PDFs regularly for review, grading, or collaboration, a desktop editor provides: all annotation types, guaranteed embedding, rich text formatting, annotation templates, flattening, and export. The time saved over struggling with multiple free tools typically justifies the one-time purchase cost.
Also Try These Free Methods
No desktop editor installed? Here are free alternatives — we list their limitations honestly.
Method 1: Microsoft Edge (Windows, Built-in)
Highlight (4 colors), draw, erase, and add text. Cannot: add sticky notes, stamps, shapes, or signatures. Annotations may not save in some versions.
Method 2: Preview (macOS, Built-in)
Highlight, underline, strikethrough, text boxes, shapes, signatures, and notes. Cannot: add stamps, callouts, or threaded comments. Annotations are embedded in the PDF.
Method 3: Adobe Acrobat Reader (Free)
Sticky notes, highlight, text comments, stamps (basic library), and drawing. Cannot: create custom stamps, flatten annotations, or export comment summaries in the free version.
Method 4: LibreOffice Draw (Free)
Shapes, text boxes, and drawing on imported PDF pages. Cannot: add standard PDF annotations — edits become content during re-export, not removable annotations.
Method Comparison: Which Should You Choose?
We tested each method on real documents to give you an honest comparison.
| Method | Annotate | Precision | Offline | Free |
|---|---|---|---|---|
| Microsoft Edge | Basic | ★★ | ✔ | ✔ |
| macOS Preview | Basic | ★★★ | ✔ | ✔ |
| Adobe Acrobat Reader | Full | ★★★★ | ✔ | ✔ |
| LibreOffice Draw | Full | ★★★ | ✔ | ✔ |
| Desktop Editor | Full | ★★★★★ | ✔ | Trial |
Verdict: Edge and Preview cover basic highlighting. For stamps, measurements, and professional markup, a desktop editor is the clear choice.
Why Desktop Editors Provide the Best Annotation Experience
Desktop PDF editors implement the full annotation specification: all annotation types, rich text formatting, custom colors, opacity control, annotation layering, flatten-to-content, and annotation export. Annotations are always embedded in the PDF, not stored in sidecar files. Desktop editors also support annotation templates — save frequently-used annotations (like a custom approval stamp) for reuse.
Free tools each cover a subset of annotation types with limited formatting. Switching between multiple free tools to access different annotation types is inefficient and produces inconsistent results. A desktop editor provides all annotation types in one consistent interface. See the full comparison →
Frequently Asked Questions
Which free tool is best for highlighting and commenting on a PDF?
For Windows: Adobe Acrobat Reader (free) provides the best combination of highlighting (multiple colors) and sticky note comments with author attribution. For macOS: Preview is excellent for highlighting (including underline and strikethrough) and adding text notes. Edge is suitable only for basic highlighting without comments.
Why do my annotations disappear when I open the PDF in a different reader?
Some viewers (particularly Edge in certain versions) save annotations in a sidecar file rather than embedding them in the PDF. When you open the PDF in a different reader, the sidecar file is not found, and the annotations appear missing. To ensure annotations are permanent, use a desktop editor that embeds them in the PDF's content, or use Acrobat Reader which always saves annotations in the PDF.
Can I flatten annotations so they become permanent content?
Yes, but only with a desktop editor. Flattening converts all annotations (highlights, comments, shapes) into permanent content objects that are part of the page. Once flattened, they cannot be edited or removed as annotations — they are indistinguishable from the original document content. This is useful for final versions of annotated documents that will be shared or archived.
Are there any limitations to this method?
Every method has trade-offs. Free built-in tools (Edge, Preview) cannot edit existing PDF text — they only add annotations or new text boxes. LibreOffice may shift complex layouts (tables, columns, images) when importing PDFs. Online tools introduce privacy risks by processing files on external servers. Desktop editors offer the most complete feature set but require a one-time purchase. For each specific task above, we have noted the most significant limitation — choose the method whose limitations you can accept for your document type. Tested on: Windows 11 24H2, macOS 15 Sequoia, PDF Agile v4.x, LibreOffice 24.x.