VB.NET PDF Editor SDK Library
How to add, edit, retrieve, delete PDF file text callout annotations using VB.NET

Dim inputFilePath As String = Program.RootPath + "\\" + "2.pdf"
Dim outputFilePath As String = Program.RootPath + "\\" + "Annot_10.pdf"

' open a PDF file
Dim doc As PDFDocument = New PDFDocument(inputFilePath)
' get the 1st page
Dim page As PDFPage = doc.GetPage(0)

' create the annotation
Dim annot As PDFAnnotTextCallout = New PDFAnnotTextCallout()

annot.StartPoint = New PointF(100.0F, 100.0F)
annot.Boundary = New RectangleF(400.0F, 500.0F, 300.0F, 80.0F)

annot.Content = "This is a text callout annotation"

' add annotation to the page
PDFAnnotHandler.AddAnnotation(page, annot)

' save to a new file
doc.Save(outputFilePath)

Dim inputFilePath As String = "C:\Annot_10.pdf"

Dim doc As PDFDocument = New PDFDocument(inputFilePath)
Dim annots = PDFAnnotHandler.GetAllAnnotations(doc)
For Each annot As IPDFAnnot In annots
    If TypeOf annot Is PDFAnnotTextCallout Then
        Dim obj As PDFAnnotTextCallout = annot
        Console.WriteLine("Textbox Boundary: " + obj.GetTextBoxBoundary().ToString())
        Console.WriteLine("Textbox Border Color: " + obj.LineColor.ToString())
        Console.WriteLine("Textbox Border Width: {0}", obj.LineWidth)
        Console.WriteLine("Textbox Fill Color: " + obj.FillColor.ToString())
        Console.WriteLine("Callout Line: ")
        For Each pt As PointF In obj.GetEndPoints()
            Console.WriteLine("  " + pt.ToString())
        Next
    End If
Next

Dim inputFilePath As String = "C:\1_Annots.pdf"

Dim doc As PDFDocument = New PDFDocument(inputFilePath)
' get all annotations in the 1st page
Dim page As PDFPage = doc.GetPage(0)
Dim annots = PDFAnnotHandler.GetAllAnnotations(page)
' remove all annotations in the 1st page
PDFAnnotHandler.DeleteAnnotation(doc, annots)