If you want to be able to scroll backwards in the file then you need to keep track of the beginning of each line. call ftell() to get the current byte location, then after reading the next line just call seek() with the location that was returned by ftell(). If you want to go back to any random line number at any time then you will want to keep an int array of the return value of ftell().
For Each ctrl As Control In Me.Controls("pnlMainPanel").Controls
If ctrl.GetType Is GetType(System.Windows.Forms.Panel) Then
For Each subCtrl As Control In ctrl.Controls
If subCtrl.GetType Is GetType(System.Windows.Forms.TextBox) Then
If subCtrl.GetType Is ...