Annotating a PDF means adding notes, highlights, and marks on top of the existing document without altering the original content. It's the standard way to review contracts, mark up research papers, give feedback on drafts, and collaborate on documents.
What Can You Add as a PDF Annotation?
| Annotation type | What it does | |---|---| | Highlight | Colour over text (yellow, green, blue, pink) | | Underline | Line under selected text | | Strikethrough | Line through text to mark for deletion | | Text box | Typed note anywhere on the page | | Sticky note / comment | Pop-up comment bubble attached to a point | | Freehand drawing | Pen/pencil for sketches and arrows | | Shape | Rectangle, circle, line, arrow | | Stamp | "APPROVED", "DRAFT", "CONFIDENTIAL" overlays | | Image | Insert a logo or screenshot |
How to Annotate a PDF with PDFlexa
Reduce your PDF file size instantly. No software needed.
- Go to Annotate PDF
- Upload your PDF
- Use the toolbar at the top to select your annotation tool:
- Highlight — click and drag over text
- Text — click anywhere and type
- Draw — freehand pen with adjustable colour and thickness
- Shapes — rectangle, circle, line, arrow
- Stamp — choose from preset stamps or create a custom one
- Click Download to save the annotated PDF
All annotations are embedded permanently in the PDF — the recipient sees them in any PDF viewer without needing special software.
Highlighting Text in a PDF
Highlighting is the most common annotation for readers and reviewers:
- Select the Highlight tool from the toolbar
- Click and drag across the text you want to highlight
- Choose a colour from the colour picker (yellow is default; green, blue, and pink available)
- The highlight appears immediately — click elsewhere to deselect and continue reading
Tip: Hold Shift while clicking to extend a selection across multiple lines.
Adding Text Comments and Notes
Turn any PDF into an editable Word document in seconds.
To leave a typed comment:
- Select the Text Box tool
- Click anywhere on the page — a text input box appears
- Type your comment
- Click outside the box to confirm
- Drag the box to reposition if needed
For longer comments tied to a specific word or passage, use the Sticky Note (comment bubble): click on the word, type your note in the popup, and the bubble icon shows in the margin. Readers click the icon to expand the full comment.
Drawing on a PDF (Arrows, Shapes, Freehand)
Useful for marking up diagrams, blueprints, and presentations:
- Arrow: Select the Arrow tool → click start point → drag to endpoint → release. Adjust colour and thickness.
- Rectangle/Oval: Drag to draw. Use for circling content or boxing sections.
- Freehand pen: Select the Pencil tool → hold and draw. Useful on touch screens and drawing tablets.
Adding a Stamp (APPROVED / DRAFT / CONFIDENTIAL)
Stamps give a document an official status mark:
- Select the Stamp tool
- Choose from preset stamps (APPROVED, DRAFT, CONFIDENTIAL, FOR REVIEW, VOID)
- Click on the page to place it
- Resize and reposition by dragging
For custom stamps (e.g., your company logo), switch to the Image annotation tool and upload a PNG with transparent background.
Annotating a PDF on Mobile
PDFlexa's annotation tools work on iOS and Android:
- Open your browser on your phone or tablet (Safari, Chrome, Firefox)
- Go to pdflexa.com → Annotate PDF
- Upload from your Files app or camera roll
- Use your finger to draw, highlight, or place text boxes
- Download the annotated PDF to share
Tip: On iPad with Apple Pencil, the freehand drawing tool is particularly accurate — excellent for markup of architectural plans or medical diagrams.
Annotating vs. Editing: What's the Difference?
| Action | Annotation | Edit | |---|---|---| | Add a note on top of text | ✅ Annotation | — | | Highlight existing text | ✅ Annotation | — | | Change existing text content | — | ✅ Edit | | Delete a page | — | ✅ Edit | | Add a watermark on every page | — | ✅ Edit (Watermark tool) | | Sign the document | Both — use Sign PDF |
Annotations sit in a separate layer above the PDF content. Editing modifies the underlying document structure.
Saving and Sharing Annotated PDFs
Once you click Download, your annotated PDF is a standard PDF file:
- Send by email as an attachment — all annotations are embedded and visible to the recipient
- Share via Google Drive, Dropbox, or OneDrive — no special viewer needed
- Print — annotations print as seen on screen
- Re-annotate — the file can be re-opened and additional annotations added
Frequently Asked Questions
Can others see my annotations? Yes. Annotations are embedded in the PDF file and visible in any PDF viewer (Adobe Acrobat, Apple Preview, browser PDF viewers, Foxit, etc.) — no special app required.
Can I remove an annotation after I've downloaded the PDF? If you still have the original un-annotated PDF, start fresh. If you've only kept the annotated version, you can try the Edit PDF tool to cover annotations with white boxes — though this is a workaround, not a true removal.
Do annotations affect the file size significantly? Minimal text annotations and highlights add almost nothing. Many freehand drawings and embedded images may add a few hundred KB per page.
Can I annotate a password-protected PDF? Only if you know the password. Use Unlock PDF first, then annotate the unlocked copy.
What colour options are available for highlights? PDFlexa supports yellow, green, blue, and pink highlights. For custom colours, use the freehand draw or shape tools with a custom colour picker.
Can I annotate a scanned PDF? Yes — annotations sit on top of the page image regardless of whether the PDF is scanned or text-based. You can highlight areas visually and add text box comments even if the underlying content is a scan.