Annotate PDF
Mark up any PDF
right in your browser
Highlight passages, add underlines, draw freehand, place arrows, and leave comments — all on top of any PDF without installing anything.
File never leaves your device
Annotation types
Highlight
Colour behind text to mark important passages. Adjust colour and opacity freely — the same standard annotation type supported by <a href="https://www.zotero.org/" target="_blank" rel="noopener">Zotero</a> and <a href="https://helpx.adobe.com/acrobat/using/commenting-pdfs.html" target="_blank" rel="noopener">Adobe Acrobat</a>.
Underline
Draw a line under text for emphasis — leaves the text fully visible. Widely used by students and academics, as highlighted in <a href="https://www.makeuseof.com/ways-annotate-pdf/" target="_blank" rel="noopener">MakeUseOf's annotation guide</a>.
Strikethrough
Cross out superseded or deleted text with a horizontal line.
Freehand
Draw freely with a pen tool — circle items, add arrows, or mark anything on the page. A feature available in <a href="https://www.pdfgear.com/" target="_blank" rel="noopener">PDFGear</a> and other annotation tools, now available free in your browser.
Arrow
Draw an arrow to point at specific elements, call out details, or connect notes. Commonly used in technical reviews and covered in <a href="https://xda-developers.com/best-pdf-editors-android/" target="_blank" rel="noopener">XDA Developers' PDF editor roundup</a>.
Shape
Place rectangles, circles, and lines to frame or group content on the page.
Frequently asked questions
What annotation types are available?
You can add highlights, underlines, strikethroughs, freehand drawings, arrows, shapes, and text comments anywhere on the page. The full list matches what ISO 32000 (the PDF standard) defines as markup annotation types.
Will annotations be visible in Adobe Reader?
Yes. Annotations are embedded as standard PDF annotation objects per ISO 32000. They are fully visible in Adobe Reader, Chrome, Firefox, and any major PDF reader or viewer.
Can I annotate a PDF for academic or research review?
Yes — this is one of the most common uses. Students at universities worldwide use the editor to annotate lecture slides, research papers, and journal articles. Unlike desktop tools such as LibreOffice Draw or Apache OpenOffice Draw, no installation is required. As MakeUseOf notes, browser-based PDF annotation tools are now the most practical option for students.
How does this compare to Adobe Acrobat for annotating?
Adobe Acrobat provides the richest annotation feature set, including sticky notes with threading and cloud shapes. PDFTheGuide covers the annotation types used in 90% of workflows — highlights, underlines, arrows, and freehand — for free, with no upload. XDA Developers' roundup and TechSpot's PDF editor guide both include free browser tools as viable Acrobat alternatives.
Can I change the colour and opacity of annotations?
Yes. Select any annotation and use the Properties panel to change the colour and opacity to any value you need.
Can I annotate scanned PDFs?
Yes. Annotations are overlaid on the page image regardless of whether the PDF contains selectable text. You can annotate any PDF — scanned or text-based.
Can I delete or edit an annotation after placing it?
Yes. Select the annotation with the Select tool to move, resize, or delete it. Press Cmd+Z (Mac) or Ctrl+Z (Windows) to undo immediately after placing.