// For complete examples and data files, please go to https://github.com/groupdocs-viewer/GroupDocs.Viewer-for-.NET
// get Configurations
ViewerConfig config = Utilities.GetConfigurations();
// create html handler
ViewerHtmlHandler htmlHandler = new ViewerHtmlHandler(config);
// guid implies that unique document name
string guid = DocumentName;
// add watermark
Watermark watermark = new Watermark("This is watermark text");
watermark.Color = Color.Red;
watermark.Position = WatermarkPosition.Diagonal;
watermark.Width = 100;
watermark.FontName = "\"Comic Sans MS\", cursive, sans-serif";
PrintableHtmlOptions printableHtmlOptions = new PrintableHtmlOptions(guid, watermark);
// get printable html in PrintableHtmlContainer
PrintableHtmlContainer container = htmlHandler.GetPrintableHtml(printableHtmlOptions);
// save html content
Utilities.SaveAsHtml(guid, container.HtmlContent);