You need to spend some time learning how to automate one application from another, especially when it comes to declaring and using variables. For example, with early binding:
Sub Demo()
Dim wdApp As New Word.Application, wdDoc As Word.Document, wdCCtrl As Word.ContentControl
Set wdDoc = wdApp.Documents.Add
With wdDoc
Set CCtrl = .ContentControls.Add(Type:=wdContentControlText, Range:=.Characters.Last)
With CCtrl
.Range.Text = "My Text"
End With
End With
End Sub
As for:
what is the appropriate reference to add in addition to the MS Word 16.0 Object Library?
Did you look for the Word object entry under Tools|References?
PS: This is not an Excel issue; it's an automation issue. I've moved the thread accordingly.