In the code from post #19, insert the two tests as shown below. The sub will stop as soon as you click on the second MsgBox. Note what the messages are. The first will give you the full path and name of the file that is opening.

'''''''''''''For testing only
MsgBox "Opening file:   " & FileNameArray(Fn)
'Exit Sub
'''''''''''''End test
             
             ''''Put all lines from one file in Arrays
            FileLinesArray = Split(.opentextfile(FileNameArray(Fn)).readall, vbCrLf)
            Formula1LinesArray = FileLinesArray
            Formula2LinesArray = FileLinesArray
             'Initializ
            Formula1Result = 0
            Formula2Result = 0
             ''''Calcuate first result for one file
             
            For Fl = 0 To UBound(FileLinesArray) - 1
'''''''''''''For testing only
MsgBox "The first line in the file is " & Formula1LinesArray(Fl)
Exit Sub
'''''''''''''End test
                 
                 '''' Calculate first formula