Annotate PDF Online for Free
Highlight PDF pages, add comments, and download the marked-up file privately in your browser.
How Do I Annotate a PDF Online for Free?
Annotating a PDF takes three steps and usually only a minute or two for a short document:
1. Select Your PDF
Click Choose PDF File and select a document from your device. The browser reads the file locally.
2. Select a Tool
Choose Highlight to mark an area or Comment to place a note. Use the color picker to organize your markup.
3. Annotate & Download
Drag to create a highlight, or click once and type a comment. Select Download PDF to save a new annotated copy.
Is This Online PDF Annotator Private?
Yes. The annotation workflow runs in your browser. The page does not send your selected PDF to a CustomizedPDF upload endpoint.
No File Upload
Your browser reads and processes the selected PDF on your device. The file is not stored on our server.
Instant, Browser-Based
PDF.js renders the pages locally, and PDF-lib creates the downloadable copy without a server-processing queue.
Free, No Account
There is no registration, paid tier, or CustomizedPDF watermark in the downloaded file.
What Is PDF Annotation?
PDF annotation means adding visual feedback—such as highlights, notes, or comments—on top of a document without rewriting its original text. It is useful for students marking readings, teachers reviewing assignments, legal or business teams flagging clauses, and anyone leaving clear feedback on a PDF.
Which annotation features does this tool support?
| Task | Supported? | How it works |
|---|---|---|
| Highlight a PDF | Yes | Drag a colored, semi-transparent box over text, an image, or any page area. |
| Add a comment | Yes | Click a position, type a note, and press Enter to save it to the output page. |
| Choose markup color | Yes | Select any color before adding a highlight or comment marker. |
| Edit existing PDF text | No | Use the free PDF editor when you need to add or change page content. |
| Create editable comment threads | No | Markup is written visibly onto the downloaded pages; it is not saved as a native, replyable PDF comment thread. |
How does the no-upload workflow work?
The implementation uses the browser's FileReader to open the PDF you select, PDF.js to render each page, and PDF-lib to write highlights and comment text into a new download. There is no PDF form submission or upload request in this workflow. The W3C File API specification explains how browsers read files that a user explicitly selects.
- Your original PDF remains unchanged.
- The downloaded copy keeps visible highlights and comment text on its pages.
- For highly sensitive documents, you should still use a trusted, updated browser on a device you control.
Capability review updated July 22, 2026. Claims above are based on inspection of this page's active annotation workflow.
Frequently Asked Questions About Annotating PDFs
Will the annotations be visible in other PDF readers?
Yes. The tool writes highlights and comment text visibly onto the downloaded PDF pages, so standard PDF readers can display them. They are flattened page content rather than native, replyable annotation objects.
Is it safe to edit my confidential documents here?
Yes. The active annotation workflow reads and processes your selected file locally in the browser; it does not upload the PDF to our server. For sensitive files, use a trusted device and an updated browser.
Can I edit the text of the PDF?
No. This tool adds highlights and comments over the existing page; it does not change the PDF's original text. Use our free PDF Editor when you need to add or change page content.
Can I highlight a scanned PDF?
Yes. Highlights are drawn over a selected page area, so they work on scanned pages and images as well as text-based PDFs. The tool does not run OCR or make scanned text searchable.
Does the downloaded PDF have a watermark?
No. CustomizedPDF does not add a watermark to the annotated copy. Any watermark already present in your original document will remain.
Do I need to install software or create an account?
No. The annotator runs in a modern web browser and does not require an account, browser extension, or desktop installation.
Further Reading
See how to annotate a PDF. Covers highlighting, comments and sticky notes, and which annotation types survive being opened in Acrobat.