' For complete examples and data files, please go to https://github.com/groupdocsannotation/GroupDocs_Annotation_NET
Try
' Get input file stream
Dim inputFile As Stream = New FileStream(CommonUtilities.MapSourceFilePath(filePath), FileMode.Open, FileAccess.ReadWrite)
' Initialize list of AnnotationInfo
Dim annotations As New List(Of AnnotationInfo)()
' Initialize text annotation.
Dim textAnnotation As New AnnotationInfo() With { _
.Box = New Rectangle(CSng(265.44), CSng(153.86), 206, 36), _
.PageNumber = 0, _
.SvgPath = "[{""x"":265.44,""y"":388.83},{""x"":472.19,""y"":388.83},{""x"": 265.44,""y"":349.14},{""x"":472.19,""y"":349.14}]", _
.Type = AnnotationType.Text, _
.CreatorName = "Anonym A." _
}
' Add annotation to list
annotations.Add(textAnnotation)
' Export annotation and save output file
CommonUtilities.SaveOutputDocument(inputFile, annotations, DocumentType.Pdf)
Catch exp As Exception
Console.WriteLine(exp.Message)
End Try