Public Class Form1
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        Dim addForm As Form
        Dim formname As String
        formname = "Form2"
        addForm = GetForm(formname)
 
        If Not addForm Is Nothing Then
            addForm.TopLevel = False
            Me.Panel1.Controls.Add(addForm)
            addForm.Show()
        End If
    End Sub
End Class

Public Class Form2
 
    Private Sub cmd_edit_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles cmd_edit.Click
        Extern_Edit(Me.TextBox1.Text)
    End Sub
End Class

Imports System.Reflection
Module Module1
    Public EditProcess As New System.Diagnostics.Process
    Delegate Sub setTextCallback(ByRef TextArray() As String)
 
    Function GetForm(ByVal FormName As String) As Form
 
        Dim AppAssembly As System.Reflection.Assembly = _
          System.Reflection.Assembly.GetExecutingAssembly
 
        Dim Formtype As Type() = AppAssembly.GetTypes
 
        Dim newForm As Form = Nothing
 
        For Each mType As Type In Formtype
 
            If mType.BaseType Is GetType(Form) AndAlso mType.Name = FormName _
              Then
 
                newForm = Activator.CreateInstance(mType)
 
                Exit For
 
            End If
 
        Next
 
        Return newForm
 
    End Function
    Public Sub Extern_Edit(ByVal strTxt As String)
        Dim f As Integer
        Dim TextFileArray() As String
        TextFileArray = strTxt.Split(vbNewLine)
 
        f = FileSystem.FreeFile()
 
        FileSystem.FileOpen(f, My.Application.Info.DirectoryPath & "\text.txt", _
          OpenMode.Output)
        If TextFileArray IsNot Nothing Then
            For Each TextFileArray_item As String In TextFileArray
                FileSystem.PrintLine(f, TextFileArray_item)
            Next TextFileArray_item
        End If
        FileSystem.FileClose(f)
 
        EditProcess.EnableRaisingEvents = True
        AddHandler EditProcess.Exited, AddressOf proc_Exited
        EditProcess.StartInfo.FileName = (My.Application.Info.DirectoryPath & _
          "\text.txt")
        EditProcess.Start()
 
    End Sub
    Private Sub proc_Exited(ByVal sender As Object, ByVal e As System.EventArgs)
        Dim TextFileArray() As String = IO.File.ReadAllLines( _
          My.Application.Info.DirectoryPath & "\text.txt")
 
        setText(TextFileArray)
    End Sub
 
    Public Sub setText(ByRef TextArray() As String)
 
        If Form2.TextBox1.InvokeRequired Then
            Dim d As New setTextCallback(AddressOf setText)
            Dim i As Integer
            For i = 0 To TextArray.GetUpperBound(0)
                Form2.Invoke(d, New Object() {TextArray(i)})
            Next i
        Else
            For i = 0 To TextArray.GetUpperBound(0)
                Form2.TextBox1.Text += TextArray(i) & vbNewLine
            Next i
            My.Application.DoEvents()
        End If
    End Sub
 
End Module