The GroupDocs.Annotation .NET SDK provides access to the GroupDocs.Annotation .NET API. The API allows developers to annotate text or images in a document. This includes uses for comments, explanations with highlighted notes, watermark, polyline and more. The Annotator API supports PDF, Microsoft Word DOCX, Excel XLSX and PowerPoint PPTX documents. GroupDocs provides document manipulation APIs that allows you to view, convert, annotate, compare, sign, assemble and search documents in your applications.