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"Annotate this PDF" can mean five different things depending on who's asking. Your professor wants you to highlight and add notes. Your boss wants a "DRAFT" stamp on every page. Your lawyer wants a signature on page 12. Your colleague wants text in the margins. This guide covers all of it, using only free tools.
PDF annotation covers several distinct actions. Each one has different free tools that handle it best:
| Annotation Type | What It Does | Best Free Tool |
|---|---|---|
| Add typed text | Place new text at a specific position | PDF Text Adder (browser) or Preview (Mac) |
| Highlight text | Yellow/green/pink highlight over existing text | Preview (Mac), Edge (Windows), Foxit Reader |
| Freehand drawing | Draw with a pen, circle things, underline | Preview (Mac), Edge (Windows), Files (iPhone) |
| Add signature | Draw or place a handwritten signature | PDF Signer (browser) or Preview (Mac) |
| Sticky notes/comments | Pop-up notes attached to specific locations | Adobe Reader (free), Foxit Reader |
| Stamp (DRAFT, CONFIDENTIAL) | Large text stamp on pages | PDF Text Adder (36pt center stamp) |
| Form filling | Type into designated form fields | PDF Form Filler (browser) |
No single free tool does all seven perfectly. The strategy is using the right tool for each type. Below is how to handle each one.
This is the most common annotation: you need to put words on a PDF page. A label, a header, a note, a name on a form that isn't fillable.
Browser-based (any device): The PDF Text Adder places text at your chosen position (top, bottom, or center) on any page or all pages. Choose from Helvetica, Times Roman, or Courier in sizes from 8pt to 36pt. Colors: black, gray, red, blue. Best for stamps, headers, footers, and labels.
Mac Preview: Open PDF > Markup Toolbar > T (Text) > drag text box anywhere > type. More precise placement than the browser tool (you can drag the box to any exact position), but only works one page at a time.
Windows Edge: Open PDF in Edge > "Add text" in toolbar > click to place text > type. Basic but functional.
For a detailed walkthrough of all text-adding methods, see our type on PDF guide or our write on PDF without Adobe guide.
Highlighting existing text in a PDF requires a tool that can detect the text layer and apply a colored overlay. This is different from adding new text.
Mac Preview: Select text with your cursor, then click the highlight button in the Markup toolbar (or right-click > Highlight). You can change highlight colors. This is the easiest free highlighting experience.
Windows Edge: Open the PDF in Edge and use the highlight tool in the toolbar. Select text and apply yellow, green, blue, or pink highlights.
Adobe Acrobat Reader (free): The free version of Acrobat Reader supports highlighting. Download it if you don't have it. This works on Windows, Mac, iOS, and Android.
Foxit Reader (free, Windows/Mac): Full highlighting toolkit with multiple colors and a persistent highlighter tool that stays active for multi-highlight sessions.
Note: Scanned PDFs (images of documents) often don't have a text layer. You can't highlight text that the PDF viewer can't detect. If you need to highlight a scanned document, first run it through OCR to add a text layer, then highlight.
Circling things, drawing arrows, underlining, or sketching on the PDF.
Mac Preview: Markup Toolbar > Sketch tool (wavy line icon). Draw freehand with your trackpad or mouse. Shapes tool adds rectangles, circles, arrows, and lines.
iPhone/iPad Files: Open PDF > Markup > use the pen, pencil, or marker tools to draw directly on the PDF. Apple Pencil makes this precise on iPad.
Windows Edge: Draw tool in the PDF toolbar. Pick ink color and thickness.
Our browser-based tools are designed for specific actions (add text, add signature, add image) rather than freehand drawing. For drawing and sketching on PDFs, the built-in platform tools (Preview, Edge, Files) are the right choice.
Two approaches: draw your signature digitally, or use a dedicated signing tool.
Browser-based: The PDF Signer lets you draw your signature on a canvas and place it on any page of a PDF. Works on every device.
Mac Preview: Markup Toolbar > Signature tool. Create your signature using the trackpad, camera (sign on paper and hold up to camera), or iPhone (sign on your iPhone screen). Preview saves it for reuse.
iPhone Files: Markup > + > Signature. Draw with your finger.
For more on signing PDFs without Adobe, see our e-signature alternatives guide.
Pop-up notes attached to specific locations in the PDF. Useful for review feedback.
Adobe Acrobat Reader (free): This is one area where the free version of Acrobat Reader actually works well. Click the comment tool, click a location on the PDF, type your note. You can also use the "Add Sticky Note" tool.
Foxit Reader (free): Same functionality. Click the note tool, place notes anywhere, type comments.
Mac Preview: Tools > Annotate > Note. Creates a yellow sticky note at the location you click.
Browser-based tools generally don't support sticky notes because note annotations require the PDF viewer to display interactive popups. Use a desktop application for this type of annotation.
CONFIDENTIAL, DRAFT, APPROVED, DO NOT DISTRIBUTE. Large text on every page.
The PDF Text Adder handles this. Type your stamp text, set it to 36pt, choose Center position, select All Pages, and color it red. One click stamps every page. See our header/footer/stamp guide for the full walkthrough.
Here's the complete free setup that replaces Adobe Acrobat Pro for annotation:
No single tool replaces everything Acrobat Pro does, but this combination covers every annotation type for free. The browser tools handle text, signatures, and forms on any device. The platform tools handle highlighting, drawing, and notes on their respective platforms.
Start annotating. Add text to your PDF right now.
Open PDF Text Adder →