A lightweight .NET library for HTML5-based document annotation. Designed for easy integration into any .NET (ASP.NET, C#, VB.NET) app, it allows end users to annotate 50+ types of files, including PDF, Microsoft Word, Excel, PowerPoint, as well as Visio, CAD and raster images.

Key features include:

1. Cross-platform compatibility. End users can view and annotate documents from any web-enabled device, including mobiles and tablets, using any HTML5-complient browser.

2. Native text rendering. Documents are rendered as text files. This allows users to select/copy and strikethrough/underline text right in documents rendered within your app or website.

3. Comprehensive set of annotation tools, including:
- Text annotation (strike-through/underline and comment on text).
- Text replacement (edit text within the document).
- Text/area redaction (blackout text/area).
- Sticky notes with rich text.
- Area annotation (comment on an area marked up with a rectangle).
- Point annotation (add notes to any point in the document).
- Polyline (draw freehand lines).
- Watermarking.
- Arrow (direct users' view to the pointed elements).
- Ruler (measure distance between objects in the document).
- Undo/redo options.

4. Convenient web UI. A customizable UI that comes with the library, allows users to seamlessly navigate and annotate large multi-page documents from a browser. Users can turn pages like slides and preview them with thumbnails, jump to a specified page or between annotations, print and export annotated documents to PDF.

5. Support for native Word and PDF annotations. GroupDocs annotations can be converted to/from native PDF or Word annotations for further offline/online editing.

GroupDocs.Annotation for .NET library doesn't require any client installation and can be deployed with a single DLL.