There are two ways to do the same thing 1st is using loop 2nd is using Input LOF statement (faster) 

'1st 
CommonDialog1.Filter = "data file(*.txt)|*.txt|all file(*.*)|*.*" 
CommonDialog1.ShowOpen 

Dim filename1 As String 
If CommonDialog1.FileName <> "" Then 
  filename1 = CommonDialog1.FileName 
  File1.Open filename1, 1 
  Dim abc As String 
  Do While Not File1.EOF 
    abc = abc & File1.LineInputString 
  Loop 
  File1.Close 

  Text1.Text = abc 
End If 
  

'2nd 

CommonDialog1.Filter = "data file(*.txt)|*.txt|all file(*.*)|*.*" 
CommonDialog1.ShowOpen 

Dim filename1 As String 
Dim abc As String 
If CommonDialog1.FileName <> "" Then 
  filename1 = CommonDialog1.FileName 
  File1.Open filename1, fsModeInput, fsAccessRead 
  abc = File1.Input(File1.LOF) 

  Text1.Text = abc 
  File1.Close 
End If 

ah yea we need to add FileSystem and, if we're going to use 
the above source code, commondialog control.