use Command() to grab command line parameters which should be the filename of the file you want to open then read it into the text box


eg:
Code:
Option Explicit

Private Sub Form_Load()
Dim filename As String
Dim fnum As Byte
Dim strtemp As String
 filename = Command()
If filename <> "" Then
  fnum = FreeFile
 
  Open filename For Binary As fnum
   strtemp = Space(LOF(fnum))
   Get fnum, , strtemp
   Close fnum
  End If
  
   Text1.Text = strtemp
End Sub