JSObject Doesn't Have Correct Commands

I changed the code in the guide slightly, it works on visual studio 2017:

Dim gApp As Acrobat.CAcroApp
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
gApp = CreateObject("AcroExch.App")
End Sub
Private Sub Form1_Closed(Cancel As Integer)
If Not gApp Is Nothing Then
gApp.Exit
End If
gApp = Nothing
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim pdDoc As Acrobat.CAcroPDDoc
Dim page As Acrobat.CAcroPDPage
Dim jso As Object
Dim path As String
Dim point(1) As Integer
Dim popupRect(3) As Integer
Dim pageRect As Object
Dim annot As Object
Dim props As Object
OpenFileDialog1.ShowDialog()
path = OpenFileDialog1.FileName
pdDoc = CreateObject("AcroExch.PDDoc")

If pdDoc.Open(path) Then
jso = pdDoc.GetJSObject
If Not jso Is Nothing Then
' Get size for page 0 and set up arrays
page = pdDoc.AcquirePage(0)
pageRect = page.GetSize
point(0) = 0
point(1) = pageRect.y
popupRect(0) = 0
popupRect(1) = pageRect.y - 100
popupRect(2) = 200
popupRect(3) = pageRect.y
' Create a new text annot
annot = jso.AddAnnot
props = annot.getProps
props.Type = "Text"
annot.setProps(props)

' Fill in a few fields
props = annot.getProps
props.page = 0
props.point = point
props.popupRect = popupRect
props.author = "Guilan Huang"
props.noteIcon = "Comment"
props.strokeColor = jso.Color.red
props.Contents = "I added this comment from Visual Basic!"
annot.setProps(props)
End If
pdDoc.Close()
MsgBox("Annotation added to " & path)
Else
MsgBox("Failed to open " & path)
End If
pdDoc = Nothing
End Sub

In addition, you'll note the explanation text on Page 25 of the IAC developer guide shows the correct capitalization of "addAnnot". So this is most likely an error in the guide.

It also explains that there is a performance issue with making multiple calls to the JSO.  Another good reason to use a folder level JS function instead of all these calls.

That's not a very good example.  There are serious problems with translating between VB objects and JS objects. You are much better off writing the functionality you want as a folder level JavaScript function, then calling this function from the JSO in VB.  Also restrict everything you pass into the JSO function calls to string and scalar values

However, I believe the specific issue with your script is that JS is case sensitive, and there are capitals in the wrong places. You also don't need to set many of the other annot properties, such as all the popup stuff. And "point" is not a property of the text annot.

Try using:

annot = jso.addAnnot

The "a" in addAnnot is lower case. The same is true for "type" and "color".

But again, I would not do any of this in the VB code. Instead I would write the functionality as a Folder Level JavaScript function and then call the function from the VB.