What Is GroupDocs.Annotation? GroupDocs.Annotation is a lightweight and powerful library which allows developers to seamlessly enhance their applications with the capability to annotate documents from wide range of supported formats. Annotations can be applied in form of textual comments, explanations with highlighted notes, watermarks, Polylines, text/resource redactions and much more. Along with ability to annotate documents multiple users can collaborate via annotation comments. Annotate PDF, DOCX/DOC, PPTX/PPT, XLSX/XLS, JPG, PNG, TIFF, VSDX/VSD, ODT, ODS, ODP, EML, HTML and many others formats, comment and review documents with GroupDocs....highlighted notes, watermarks, polylines, text/resource redactions...