Annotate PDF Online
Highlight, underline, comment, draw on PDFs in your browser. Saves annotations as standard PDF markups. Free, no signup.
About PDF Annotator
PDF Annotator lets you add highlights, sticky notes, freehand drawings, text boxes, stamps, and geometric shapes directly on PDF pages — all in your browser via pdf-lib and the Canvas API. Annotations are embedded as proper PDF annotation objects (not flattened image overlays), so recipients who open the annotated PDF in Acrobat Reader, macOS Preview, or any standards-compliant viewer see the annotations as interactive elements they can hover, click, and reply to. Highlights use PDF's native highlight annotation type, preserving the ability to copy the highlighted text.
Most browser annotation tools flatten annotations — they draw colored boxes directly on the page image, making the annotation permanent and the text underneath no longer selectable. This tool writes proper PDF annotation objects: a yellow highlight stays a highlight annotation, a sticky note stays a note annotation with a hover-to-read tooltip, and the underlying text remains selectable and searchable. The PDF standard annotation model also means annotations are included in PDF text search and can be exported as an FDF/XFDF annotation report for legal review workflows.
How to Use Annotate PDF Online
- Step 1: Open your PDF in the annotator. All existing annotations (from Acrobat or other tools) are loaded and displayed.
- Step 2: Select a tool from the toolbar: highlight (drag over text), sticky note (click to place), draw (freehand), text box, shape, or stamp.
- Step 3: For highlights, drag across the text you want to mark. The highlight appears immediately and the original text stays selectable.
- Step 4: For sticky notes, click the target location, type your note, and press Enter. Hover to read; click to edit or delete.
- Step 5: When done, click Save Annotated PDF. Annotations are written as proper PDF objects. Download and share the annotated file.
Key Features
- Highlight — PDF-native highlight annotations, 8 colors, text remains selectable and searchable
- Sticky notes — hover-to-read popup notes attached to any page location
- Freehand drawing — smooth stroke rendering with pressure simulation for natural annotation feel
- Text boxes — typed text overlay with font, size, and color control
- Geometric shapes — rectangles, circles, lines, and arrows with stroke color, fill color, and opacity
- Stamps — APPROVED, REJECTED, DRAFT, CONFIDENTIAL, and custom text stamps
- PDF-native annotation objects — not flattened; interactive in Acrobat, Preview, and other viewers
- Annotation export — export an FDF annotation report separate from the PDF for legal workflows
How We Compare
Compared to desktop alternatives like Adobe Acrobat Pro (starting at $19.99/month), Smallpdf ($12/month for unlimited), or iLovePDF ($9/month Premium), PDF AI Tools delivers comparable quality at $0 for the core feature set. We skip the subscription friction by processing most operations directly in your browser with WebAssembly — no server infrastructure costs to pass on to users. Our AI features (summarization, chat, OCR) use a pay-as-you-go backend that keeps your total cost well under $5/month even for power users.
Frequently Asked Questions
Can recipients see my annotations in Adobe Reader?
Yes — annotations are written as PDF-standard annotation objects, fully compatible with Adobe Acrobat Reader, macOS Preview, Foxit Reader, and any ISO 32000-compliant PDF viewer. Highlights, sticky notes, and shapes all display as interactive elements.
Are my annotations permanent or can they be removed?
PDF annotation objects are separate from the page content — they can be individually deleted by anyone with the annotated PDF. To make annotations permanent (unable to remove), use the Flatten Annotations option before downloading: this burns annotations into the page image stream.
Can I annotate a password-protected PDF?
Only if you supply the correct password to open the file. After unlocking, annotations work normally. If the PDF has permission restrictions that block editing, the annotation layer is saved but some viewers may refuse to display editable annotations — use the flatten option to embed them as content instead.
What is an FDF annotation export and when do I need it?
FDF (Forms Data Format) is a PDF-standard format for exporting just the annotation data separately from the document. It is used in legal document review workflows where annotations are submitted to a review platform that merges annotations from multiple reviewers. Most individual users don't need FDF — the annotated PDF itself is sufficient.
Can I collaborate with others on annotations?
Not in real time — this tool is for single-user annotation. For multi-user annotation workflows (legal review, academic peer review), you each annotate your own copy and merge annotations using a PDF review platform that accepts FDF imports.
Who Uses This Tool
- Lawyers marking up contract drafts with highlights and comments for client review
- Academics annotating research papers with sticky notes and margin comments
- Designers reviewing proof PDFs with shape annotations marking layout corrections
- Students highlighting key sections in PDF textbooks and adding study notes
- HR managers marking up job applications and interview scorecards
- Quality assurance teams stamping engineering drawings APPROVED or REJECTED with annotations