Public Class Form1
 
    Declare Function OemToCharBuff Lib "user32" Alias "OemToCharBuffA" (ByVal _
      lpszSrc As String, ByVal lpszDst As String, ByVal cchDstLength As _
      Integer) As Integer
    Declare Function CharToOemBuff Lib "user32" Alias "CharToOemBuffA" (ByVal _
    lpszSrc As String, ByVal lpszDst As String, ByVal cchDstLength As Integer) _
    As Integer
 
    Dim file_name As String = ""
    Private Sub btn_browse_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles btn_browse.Click
        dlg_file_open.ShowDialog()
    End Sub
 
    Private Sub dlg_file_open_FileOk(ByVal sender As System.Object, ByVal e As _
      System.ComponentModel.CancelEventArgs) Handles dlg_file_open.FileOk
        rtb_text.Clear()
        file_name = dlg_file_open.FileName
        txt_path.Text = file_name
 
        Dim StmReader As New StreamReader(file_name, False)
        Dim strline As String = ""
 
        While (StmReader.Peek() <> -1)
            strline = StmReader.ReadLine()
            ANSItoASCII(strline)
            'ASCIItoANSI(strline)
            rtb_text.AppendText(strline)
        End While
 
        StmReader.Close()
    End Sub
    Function ASCIItoANSI(ByVal Text As String) As String
        Dim strRet As String = New String("  ", Text.Length)
        OemToCharBuff(Text, strRet, Text.Length)
        MessageBox.Show(strRet)
        Return strRet
    End Function
    Function ANSItoASCII(ByVal Text As String) As String
        Dim strRet As String = New String(" ", Text.Length)
        CharToOemBuff(Text, strRet, Text.Length)
        MessageBox.Show(strRet)
        Return strRet
    End Function