Visual Basic

Imports System.IO

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click


        Dim find As String = "String To Find"
        Dim replace As String = "String To Replace"
        Dim path As String = "c:\InputPath.doc"
        Dim updatedpath As String = "c:\OutputPath.doc"
        Dim encoding As System.Text.Encoding = System.Text.Encoding.GetEncoding(1252)

        Dim fi As New FileInfo(path)

        Dim fs As New FileStream(path, FileMode.Open)

        Dim bytes(CInt(fs.Length)) As Byte

        fs.Read(bytes, 0, CInt(fs.Length))
        fs.Close()

        Dim newBytes() As Byte = DoReplace(bytes, encoding.GetBytes(find), encoding.GetBytes(replace))

        fs = New FileStream(updatedpath, FileMode.Create)
        fs.Write(newBytes, 0, newBytes.Length)
        fs.Close()

    End Sub

    Public Function DoReplace(ByVal bytes As Byte(), ByVal findBytes As Byte(), ByVal replaceBytes() As Byte) As Byte()

        Dim newBytes As New Generic.List(Of Byte)
        Dim ndx As Integer = 0

        For x As Integer = 0 To bytes.Length - 1
            ' bytes is the original files bytes 
            If bytes(x) = findBytes(ndx) Then
                ' findBytes is a byte[] from the"find" string 
                If ndx = (findBytes.Length - 1) Then
                    For y As Integer = 0 To replaceBytes.Length - 1
                        'replaceBytes is a byte[] from the "replace" string 
                        newBytes.Add(replaceBytes(y))
                    Next
                    ndx = 0
                Else
                    ndx += 1
                End If
            Else
                If ndx > 0 Then
                    For y As Integer = 0 To ndx - 1
                        newBytes.Add(findBytes(y))
                    Next
                End If
                ndx = 0
                newBytes.Add(bytes(x))
            End If
        Next

        Return newBytes.ToArray

    End Function
End Class