How to Highlight a PDF — Free Annotation Guide (2026)
By PDFKits Team — Published July 2, 2026
How to Highlight a PDF on Mac (Preview)
Mac users have a powerful built-in PDF annotation tool in Preview. Highlighting text in Preview is straightforward and requires no additional software:
Open the PDF in Preview (right-click the file → Open With → Preview, or just double-click if Preview is your default PDF viewer).
Click the Highlight button in the toolbar. It looks like a marker pen or crayon icon. If you do not see it, click View → Show Markup Toolbar first.
Select the text you want to highlight by clicking and dragging over it.
The text is highlighted in yellow by default. To change the color, click the dropdown arrow next to the highlight button and choose from yellow, green, blue, pink, or purple.
To remove a highlight, click on the highlighted text and press the Delete key.
Preview also supports underline and strikethrough annotations from the same toolbar. You can highlight an entire document by selecting all text (Cmd+A) and then clicking the highlight button, though this is rarely needed. Your highlights are saved automatically when you close the file — there is no separate save step required.
How to Highlight a PDF on Windows
Windows does not include a built-in PDF highlighter as capable as Mac Preview, but Microsoft Edge provides a solid free option:
Using Microsoft Edge
Right-click the PDF file and select Open with → Microsoft Edge.
The PDF opens with Edge's built-in reader and a toolbar appears at the top.
Click the Highlight button (marker icon) in the toolbar.
Select the text you want to highlight by clicking and dragging.
Choose a highlight color from the color picker that appears.
To save, press Ctrl+S or click the save icon. Edge saves the highlights directly into the PDF file.
Using Google Chrome
Chrome's built-in PDF viewer does not support highlighting natively. However, you can install free browser extensions that add highlight functionality, or use an online tool like PDFKits Annotate PDF for full annotation capabilities without installing any extensions.
For a more full-featured desktop experience on Windows, free PDF readers like Foxit Reader and SumatraPDF also offer highlighting tools built into their interfaces.
How to Highlight a PDF Online (Free)
For a platform-independent highlighting experience, use the PDFKits Annotate PDF tool. This works in any browser on any device:
Upload your PDF file by clicking the upload area or dragging the file in.
Select the highlight tool from the annotation toolbar.
Choose your preferred highlight color.
Click and drag over the text you want to highlight.
Add as many highlights as you need across all pages of the document.
Click Download to save the annotated PDF.
PDFKits processes everything in your browser — your PDF is never uploaded to a server. This makes it safe for highlighting confidential documents, contracts, and sensitive materials. No account is required and there are no watermarks on the downloaded file.
How to Highlight a PDF on iPhone and iPad
iOS and iPadOS include built-in PDF annotation tools in the Files app and Books app:
Using the Files App
Save or open the PDF in the Files app.
Tap the PDF to open it.
Tap the Markup icon (a pen tip inside a circle) in the top-right corner.
Select the highlight tool from the markup toolbar (the Aa icon or the marker icon, depending on your iOS version).
Tap and drag over the text you want to highlight.
Tap Done when finished. Your highlights are saved automatically.
Using Apple Books
Open the PDF in the Books app.
Press and hold on any word to select it, then drag the selection handles to highlight a passage.
A menu appears with a Highlight option. Tap it to apply the highlight.
Choose a color from the color options that appear.
On iPad, you can also use the Apple Pencil to draw freehand highlights directly on the PDF page using the Markup tools. This is especially useful for highlighting content in scanned PDFs where text selection may not work.
Color-Coding System for PDF Highlights
Using different highlight colors strategically transforms highlighting from a simple annotation into a powerful organizational system. Here is a widely-used color-coding scheme for academic research, legal review, and professional document analysis:
Yellow — Key points and definitions: Use yellow for the most important concepts, definitions, and central arguments. Yellow is the default highlight color in most tools because it is the most visible without being distracting.
Green — Agreed or approved: Use green to mark content you agree with, approve of, or want to keep. In collaborative editing, green often signals "this is good" or "approved as-is."
Pink or Red — Important warnings: Use pink for critical warnings, potential issues, disputed claims, or content that needs attention or correction. In legal review, pink often marks clauses that need revision.
Blue — References and citations: Use blue for source references, citations, statistics, and evidence. This makes it easy to trace back claims to their supporting data when reviewing later.
Orange — Action items: Use orange for tasks, deadlines, follow-up items, and content that requires a response or action. Orange stands out as "do something about this."
Consistently applying a color system across all your PDFs makes it much easier to review documents later, especially when working with long reports, textbooks, or multi-document research projects.
How to Highlight a Scanned PDF
Scanned PDFs are essentially images wrapped in a PDF container. Because the text is not digitally encoded (it is just a picture of text), standard text selection and highlighting tools will not work. You have two options:
Use OCR (Optical Character Recognition): OCR software scans the image and recognizes the text, creating a selectable text layer on top of the image. After OCR processing, you can highlight text normally. Many PDF editors and online tools offer built-in OCR functionality.
Use freehand drawing or shape tools: If OCR is not available, you can use rectangle or freehand drawing tools to draw colored shapes over the text you want to highlight. Set the shape to a semi-transparent yellow (or other color) to simulate a highlight effect. Both Preview on Mac and the PDFKits Annotate PDF tool support freehand drawing.
If you need to extract the actual text content from a scanned PDF, use PDFKits PDF to Text which includes text extraction capabilities for digital PDFs.
Beyond Highlighting — Other PDF Annotations
Highlighting is just one of many annotation types available for PDF documents. Depending on your needs, consider using these additional markup tools:
Text comments: Add typed notes at specific locations in the document. Useful for providing feedback or explanations.
Sticky notes: Attach expandable notes that collapse to a small icon, keeping the document clean while preserving detailed comments.
Underline: Emphasize text without the visual weight of a full highlight. Good for secondary important points.
Strikethrough: Mark text for deletion or indicate disagreement. Commonly used in editing and proofreading workflows.
Drawing tools: Add freehand drawings, arrows, circles, and other shapes to call attention to specific areas of the document.
Stamps: Apply predefined stamps like "Approved," "Draft," "Confidential," or "Reviewed" to pages. Useful for document workflow status tracking.
For comprehensive PDF editing beyond annotations, use PDFKits Edit PDF to add text, images, and modify page content. For digital signatures, use PDFKits Sign PDF to sign documents electronically. You can also add visual watermarks to your PDFs using PDFKits Add Watermark for branding or confidentiality purposes.
On Mac, use the built-in Preview app (click the highlight button in the toolbar, then select text). On Windows, open the PDF in Microsoft Edge and use its built-in highlight tool. On any platform, use PDFKits Annotate PDF in your browser for free highlighting with no account required.
Can I highlight a PDF without Adobe Acrobat?
Yes. Adobe Acrobat is not required for highlighting PDFs. Mac Preview, Microsoft Edge, and free online tools like PDFKits Annotate PDF all offer PDF highlighting at no cost. Many free PDF readers on both Windows and Mac also include highlighting capabilities.
How can I highlight a PDF on my phone?
On iPhone and iPad, open the PDF in the Files app and tap the Markup icon to access highlighting tools. On Android, use the Google Drive PDF viewer or download a free PDF reader like Adobe Acrobat Reader (free version) or Xodo. You can also use PDFKits Annotate PDF in your mobile browser for a consistent experience across all devices.
How do I remove highlights from a PDF?
In Preview on Mac, click the highlighted text and press Delete. In Edge on Windows, right-click the highlight and select Delete. In most PDF editors, right-clicking or tapping a highlight reveals a delete or remove option. Note that if a PDF has been flattened, highlights become permanent and cannot be removed.
Can you highlight a scanned PDF?
Standard text highlighting does not work on scanned PDFs because the text is an image, not selectable text. You have two options: run OCR (optical character recognition) to create a text layer, then highlight normally; or use freehand drawing tools to draw semi-transparent colored shapes over the text areas you want to emphasize.