Dim Richtextbox1 As New RichTextBox
Richtextbox1.LoadFile("Pfad/Name der RTF Datei")
 
Dim searchTerm As String = "Regelung"
Dim anz As Integer = CountWord(richtextbox1.Text, searchTerm)
 
Dim wordindex As Integer = -1, counter As Integer = 0
 
Do
 
   wordindex = Richtextbox1.Find_
    (searchTerm, wordindex + 1, RichTextBoxFinds.WholeWord)
 
   If Not wordindex = -1 Then
      Richtextbox1.SelectionStart = wordindex
      counter += 1
   End If
 
Loop While Not wordindex = -1

Public Function CountWord(ByVal text As String, _
            ByVal wordtocount As String) As Integer
 
    If String.IsNullOrWhiteSpace(text) Then Return -1
    If String.IsNullOrWhiteSpace(wordtocount) Then Return -1
 
    wordtocount = GetWord(wordtocount)
 
    Dim splitchars As String = " ,;.:?!"
 
    Dim dataSource As String() = _
     text.Split(splitchars.ToArray, _
     StringSplitOptions.RemoveEmptyEntries)
 
    Dim matchquery As IEnumerable(Of String) = _
     From word As String In dataSource _
     Where String.Compare(GetWord(word), wordtocount, True) = 0
 
    Return matchquery.Count()
 
End Function
 
 
 
Private Function GetWord(ByVal word As String) As String
 
    If String.IsNullOrWhiteSpace(word) Then Return String.Empty
 
    Dim trimchars As String = "<>[]{}()+-*/\|@#"
 
    word = word.Trim(trimchars.ToArray)
 
    Return word
 
End Function

Dim anz As Integer = CountWord(Richtextbox1.Text, searchTerm)