Try this code. I use this code to open text file then put the filename in the textbox
.Filter = "Text files (*.txt)|*.txt|" & "All files|*.*"
'setting filters so that Text files and All Files choice appears in
'the Files of Type box in the dialog
If .ShowDialog() = DialogResult.OK Then
'showDialog method makes the dialog box visible at run time
Textbox1.Text = .FileName