Private Sub btn1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn1.Click

        Dim stream As FileStream

        ' Open file for reading and writing simultaneously
        stream = New FileStream("c:\\testing.txt", FileMode.Open, FileAccess.ReadWrite)

        ' Lets move to position four from the beginning of the file
        stream.Seek(4, SeekOrigin.Begin)

        ' Using an encoding (text files), read the textbox (text1) and write to stream at position specified above.
        Dim uniEncode As New System.Text.ASCIIEncoding
        stream.Write(uniEncode.GetBytes(text1.Text), 0, uniEncode.GetByteCount(text1.Text))

        ' Lets setup a byte array to read some of our text
        ' Make sure your byte array is big enough, here we only read about 10 test characters so 256 is enough.
        Dim ByteArray(256) As Byte

        ' Reset our position back to beginning of file
        stream.Position = 0

        ' Read the stream and place in array from 0 position onwards
        stream.Read(ByteArray, 0, 256)

        ' Close stream
        stream.Close()

        ' Show what was read
        MessageBox.Show(uniEncode.GetString(ByteArray))


    End Sub