Is my PDF file secure?

Yes. All processing happens in your browser. Your PDF never leaves your device and is not uploaded to any server.

Can I annotate multiple pages?

Yes. Navigate through the pages and add annotations to any page. All annotations are saved when you download.

What annotation types are supported?

You can add text annotations, highlight rectangles, freehand drawings, and use the eraser tool to remove annotations.

Does this tool work with scanned PDFs?

This tool works with all standard PDF files. For scanned documents (image-only PDFs), text extraction features may be limited since the content is stored as images rather than selectable text.

Annotate PDF Online

Add text annotations, highlights, and sticky notes directly to your PDF. Draw, highlight text, add comments, and mark up your documents with a full suite of annotation tools.

Your files never leave your device

Drop PDF here or click to browse

Supports PDF · up to 100 MB

How It Works

Upload your PDF file using the drop zone above.
Select an annotation tool from the toolbar (Text, Highlight, Draw, or Eraser).
Customize the color, brush size, and font size to match your preferences.
Click or drag on the PDF page to add annotations.
Navigate between pages using the Previous/Next buttons to annotate multiple pages.
Click "Save & Download PDF" to embed all annotations into your PDF and download it.

Why Annotate PDFs?

PDF annotations are essential for document review, collaboration, and feedback. Whether you're reviewing contracts, grading assignments, marking up designs, or providing feedback on documents, annotations help you communicate clearly and organize your thoughts. This tool lets you add professional annotations directly to your PDFs without needing expensive software.

Annotation Features

Text Annotations · Add sticky note-style text annotations anywhere on the page. Click to place, type your comment, and customize the font size.
Highlights · Create highlight rectangles in any color to mark important sections of text or areas of your PDF.
Freehand Drawing · Draw directly on the PDF with a customizable brush size. Perfect for sketches, diagrams, and markup.
Eraser · Remove annotations easily with the eraser tool without affecting the original PDF content.
Color Picker · Choose any color from the color picker to match your annotation style and preferences.
Multiple Pages · Navigate through all pages of your PDF and annotate each one individually.
Opacity Control · Adjust the opacity of your annotations from 0-100% for subtle or prominent markups.
Save & Download · Embed all annotations into the PDF and download your marked-up document.

Frequently Asked Questions

Are my annotations saved securely?

Yes. All annotations are processed in your browser and embedded into the PDF when you download it. Your original PDF is never uploaded to any server, and all processing happens on your device.

Can I annotate all pages of a PDF?

Yes. Use the page navigation buttons to move between pages. Each page can have its own annotations. All annotations are saved when you download the PDF.

Can I undo or erase annotations?

Yes. Use the Eraser tool to remove individual annotations from the current page. You can also use the "Clear Page" button to remove all annotations from the current page.

What file formats are supported?

This tool supports standard PDF files (.pdf). The annotated file is downloaded as a PDF, which is compatible with all PDF readers and viewers.

Are there size limits for PDF files?

You can upload PDF files up to 100 MB. Very large files may take longer to load and process. For best performance, keep files under 50 MB.

What is a PDF annotation tool?

A PDF annotation tool lets you add notes, highlights, drawings and comments to an existing PDF without changing its underlying text or layout. Annotations sit in a separate layer on top of the document, the way a transparent sheet would sit on top of a printed page. You can review a contract, mark up a manuscript, give feedback on a design proof or grade an assignment without ever editing the original content. When you save the PDF, the annotations are written back into the file so anyone who opens it later sees the same marks you made.

This tool gives you four core annotation types: text notes (sticky-note style comments anchored to a point on the page), highlights (coloured rectangles drawn over text or other regions), freehand drawings (pen strokes for circling, arrows, sketches) and an eraser (to remove marks you made earlier). Each annotation has adjustable colour, brush size, font size and opacity, so a soft yellow highlight, a thick red circle and a faint blue underline all coexist on the same page without fighting each other.

Everything runs in your browser. The PDF is rendered to a canvas using pdf.js (Mozilla's open-source PDF renderer), and the annotations are drawn on a transparent canvas layered on top. When you click Save, pdf-lib (a JavaScript PDF library) embeds the annotation drawings into the PDF file and returns a new file for download. No upload, no cloud, no account. The tool works with PDFs up to 100 MB and handles documents of any page count, from a one-page invoice to a multi-hundred-page manual.

What is inside the tool

The top of the interface is a drop zone where you drag a PDF in or click to browse. As soon as the file loads, the first page renders in the preview area below and the page navigation appears. The page counter tells you how many pages are in the document, and the Previous and Next buttons walk you through them. Each page is its own canvas, so annotations made on page 3 do not bleed into page 4.

Below the preview, the annotation toolbar groups the four tools: Text, Highlight, Draw and Eraser. Only one is active at a time and the active tool is shown with a coloured border. The settings panel next to the toolbar controls colour (a full HTML colour picker), brush size (1 to 20 pixels for draw and highlight strokes), font size (8 to 36 points for text notes) and opacity (0 to 100 percent for all annotations). Adjustments take effect immediately on the next mark you make and do not retro-apply to earlier marks.

Clearing is two-step on purpose. Clear Page removes every annotation from the current page only, leaving the rest of the document untouched. Clear PDF dumps the entire annotation layer and the loaded file, which is useful when you want to start over with a different document. Save and Download flattens the annotation layer into the PDF, embedding each mark as a PDF drawing primitive, and triggers a normal browser download with the annotated file.

History and background

Adobe Acrobat introduces PDF annotation (1996)

Adobe shipped Acrobat 3.0 in November 1996 and introduced the Comment Tools: sticky notes, highlights, underlines, strikethroughs and freehand pencil marks. Before Acrobat 3.0, PDFs were a static viewer-only format. After 3.0, they became a review-and-comment medium, and the legal, publishing and engineering industries began moving paper-based review workflows into PDF. The annotation types we still use today (sticky note, highlight, ink, square, free text) trace back to that release.

PDF annotation in the ISO standard (2008)

When PDF became an ISO standard (ISO 32000-1 in 2008), annotations got a formal specification: section 12.5 of the standard defines 26 annotation subtypes (Text, Link, FreeText, Line, Square, Circle, Polygon, Highlight, Underline, Squiggly, StrikeOut, Stamp, Caret, Ink, Popup, FileAttachment, Sound, Movie, Widget, Screen, PrinterMark, TrapNet, Watermark, 3D, Redact). Each has well-defined data structures, so any conforming PDF reader can render annotations made by any conforming PDF writer. This standardisation is why an annotation you make in this tool will display correctly in Adobe Reader, Foxit, Preview, Edge and any other compliant viewer.

Foxit and lighter alternatives (2001 onwards)

Foxit Reader launched in 2001 as a faster, lighter alternative to Adobe Reader and added annotation tools in subsequent versions. PDF-XChange Viewer (2008) and Nitro PDF (2005) followed similar paths: full-featured annotation without the weight of Acrobat. These tools brought annotation to users who could not afford Adobe Acrobat Pro or did not need its full editing suite. They remain popular for document-heavy professions where annotation is the daily workflow but text-level editing is rare.

Hypothes.is and web-native annotation (2011)

Hypothes.is launched in 2011 as a non-profit project to bring annotation to the open web. The idea: any document on the web, including PDFs hosted online, should be annotable in a browser without installing software. Hypothes.is and similar projects (Diigo, Genius, Pundit) pioneered the web annotation pattern that browser-native PDF annotation tools build on. The W3C Web Annotation Working Group standardised the data model in 2017, giving browser-based annotation a formal interoperability spec.

pdf.js brings PDF rendering to the browser (2013)

Mozilla shipped pdf.js as the default PDF viewer in Firefox 19 in February 2013. pdf.js is a JavaScript implementation of the PDF rendering pipeline that runs entirely in the browser, no plugin required. Chrome integrated PDFium (C++, derived from Foxit) around the same time. Once browsers could render PDFs natively, building a browser-based PDF annotator became feasible: pdf.js handles the rendering, an HTML canvas handles the annotation layer, and JavaScript ties them together. This tool follows that lineage directly.

pdf-lib enables client-side PDF editing (2018)

pdf.js can render PDFs but cannot edit them. pdf-lib, released in 2018 by Andrew Dillon, filled that gap: a JavaScript library that creates and modifies PDFs in the browser, including embedding annotations, drawing shapes, inserting text and saving the result as a new PDF file. The combination of pdf.js (render) plus pdf-lib (edit) is the standard stack for browser-based PDF tools today, including this annotator. It is what makes truly client-side, zero-upload PDF editing practical.

Practical workflows

Contract redline review

A lawyer or contracts manager receives a draft contract and wants to flag specific clauses for the counterparty. Open the PDF, highlight the clauses to discuss in yellow, add sticky-note text comments next to each highlight explaining the concern, and circle key dates or numbers with the draw tool. Save and email the annotated PDF back. The recipient sees every mark exactly where you placed it, regardless of which PDF reader they use. This is faster than Word redlines for fixed-layout documents and survives format conversions that often break Word track-changes.

Academic paper markup for review

A reviewer for a journal or conference annotates a submitted manuscript: highlight the central claim, sticky-note questions about specific arguments, circle figure numbers that need re-rendering, underline citations to check. The annotated PDF goes back to the editor or directly to the authors. Compared to writing a separate review document, in-line annotations are anchored to the exact passage they discuss, which removes ambiguity about which sentence the comment refers to.

Manuscript editing for writers

A copy editor reviewing a manuscript PDF marks every line that needs work: highlight queries, sticky-note suggested rewrites, draw to indicate paragraph breaks or restructuring. The author opens the annotated PDF, addresses each mark in the source document and replies. This workflow is common in publishing where the author works in Word or LaTeX, the editor works in PDF, and the annotations bridge the two formats. The PDF acts as a stable artifact that does not lose comments when the source file is rebuilt.

Construction and engineering drawing markup

Architects, engineers and construction managers regularly mark up site drawings: circle areas that need rework, sticky-note dimension corrections, draw arrows linking comments to specific structural elements. PDFs of CAD drawings carry the source dimensions and the markup carries the human commentary. Field teams open the annotated PDF on tablets, see exactly which beam or wall is in question, and report back with their own annotations. This is the industry-standard alternative to printing drawings and marking them up with a red pen.

Teacher feedback on student PDFs

A teacher grading student work in PDF form (essays, lab reports, problem sets) highlights mistakes, sticky-notes explanations, circles answers that need rework. The annotated PDF returns to the student with feedback anchored to the exact spot it applies to, which is far more useful than a single overall grade or a separate comments document. For online courses delivered through Moodle, Canvas or Google Classroom, the annotated PDF uploads back through the same submission interface.

Legal discovery and evidence review

In e-discovery, attorneys review thousands of PDFs (contracts, emails saved to PDF, deposition transcripts) looking for relevant passages. Highlight the relevant text in a colour-coded scheme (yellow for general relevance, red for hot documents, blue for privileged), add sticky notes explaining why a passage matters, and save the annotated PDF to the case file. Senior attorneys review the marked PDFs faster than they could read the originals because the annotations cue their attention to the parts that matter.

Common pitfalls

Flattened annotations lose editability

When this tool saves the annotated PDF, it flattens the annotations into the page content. The annotated PDF displays correctly in every viewer, but the original separate annotation layer is gone. If the recipient wants to edit your sticky notes or remove a highlight, they cannot, because the marks are now part of the page rather than a separate overlay. If you want editable annotations downstream, keep the source PDF without flattening and pass that to a tool that preserves the annotation dictionary as separate objects (Acrobat Pro, Foxit Phantom).

Viewer compatibility differs by annotation type

Not every PDF reader renders every annotation type identically. Sticky-note text and highlights are universally supported because they map to ISO 32000 standard subtypes. Custom drawings encoded as Ink annotations render slightly differently across viewers due to stroke smoothing, anti-aliasing and opacity handling. If you flatten the annotations into the page (this tool does this by default on save), the rendering becomes deterministic because the marks are part of the page content. If you keep them as separate annotations, expect minor visual differences across readers.

Annotations sit above the original text, not replacing it

A highlight is a coloured rectangle drawn on top of the text, not a property of the text itself. A draw stroke that crosses out a sentence does not delete that sentence from the document, it just paints over it. If the recipient copies and pastes text from the annotated PDF, they get the original text, not your strikethrough or your inserted sticky note. This is intentional for review workflows (you do not want annotations corrupting the source) but surprises users who expect annotations to behave like Word's track-changes deletes.

Low-contrast highlight colours are hard to read

A pale-grey highlight over black text on a white page meets WCAG contrast guidelines for the highlight itself, but the highlighted text can become harder to read because the contrast between text and highlight is now low. A dark-blue highlight over black text is the opposite problem: the highlight obscures the text. For accessibility, use light pastels (yellow, light green, peach) with low opacity for highlight rectangles, and reserve dark or saturated colours for outlines and freehand marks where they sit beside the text rather than over it.

Sticky-note placement is page-relative, not viewport-relative

When you place a sticky note at a specific spot on the page, it stays anchored to that page coordinate regardless of the zoom level the next viewer uses. That is the desired behaviour. The pitfall is that on a small mobile screen the sticky-note text may render at a tiny font size or get clipped by the page edge. Test the annotated PDF at the zoom level your recipients are likely to use, and avoid placing sticky notes too close to margins where they may overflow off-page.

Permission flags can disable annotation in downstream viewers

PDFs can be created with permission flags that disable annotation (the source author set Modification or Annotation rights to no). This tool will still let you mark up the rendered pages because the rendering happens client-side and bypasses the permission flag at render time. The downstream issue is that Adobe Reader and other compliant readers honour the permission flag when displaying the file, which can lead to inconsistent behaviour. If you control the source PDF, remove the restriction with the PDF unlock tool before annotating.

Privacy and data handling

The PDF you load and the annotations you draw never leave your device. pdf.js renders the document client-side, the annotation canvas is a browser-only HTML element, and pdf-lib embeds the final annotations into a new PDF file that the browser downloads directly to your disk. No file content is uploaded, no network request is made with the document, and no telemetry is logged about what you annotated. This matters because the documents that most need annotation (contracts, legal correspondence, medical reports, internal memos) are the same documents you should never send to a third-party processor.

Once the tool page has loaded in your browser, you can disconnect from the internet and continue annotating. The libraries are already in memory, the PDF rendering is local, and the file save is a browser-initiated download. Many users with confidential workflows annotate online tools offline for exactly this reason: no chance of accidental upload, no chance of network logging, no chance of a third-party seeing what they marked.

When not to use this tool

For permanent text edits (use PDF to Word)

Annotations sit on top of the text; they do not change the text. If you need to actually delete a word, correct a typo or rewrite a paragraph in the source PDF, this tool is the wrong choice. Convert the PDF to an editable format with PDF to Word, make the changes there, then re-export to PDF. Trying to fake text edits with strikethrough annotations and inserted sticky notes works for review but produces a confusing document for anyone trying to read the final text cleanly.

For redacting sensitive information (use PDF Redact)

Drawing a black rectangle over a sensitive name with the highlight or draw tool hides the name visually but does not delete it from the PDF. The underlying text is still extractable by anyone who copies and pastes from the document, or by any OCR or text-extraction tool. For actual redaction (removing the text from the document permanently), use the PDF Redact tool, which deletes the content rather than covering it. Annotation-based covering has been the source of multiple high-profile data-leak incidents (legal filings, government documents).

For form filling

If the PDF is a form with interactive fields (text boxes, checkboxes, signature areas), use a PDF form-filler. Annotating over a form field with a sticky-note or a text annotation does not actually fill the field; it just paints over the form widget. Recipients who open the form in Acrobat will see the empty fields next to your sticky notes, which is confusing. For real form data entry, open the PDF in Adobe Reader or Foxit and use the form-fill workflow, then save the filled form.

For legally-binding digital signatures (use PDF Sign)

Drawing a signature shape with the freehand draw tool produces a visual mark that looks like a signature but carries no cryptographic guarantee of who drew it. Legally-binding digital signatures use public-key cryptography to bind the signer's identity to the document; tampering with the document invalidates the signature. For that level of assurance use the PDF Sign tool (or a qualified signature service such as DocuSign, Adobe Sign). Reserve drawn-signature annotation for informal use only.