Sub test()
Dim wb As Workbook, F As Worksheet
For Each wb In Workbooks
If wb.Name Like "NomClasseur*" Then
For Each F In wb.Worksheets
F.Activate
F.Columns("C:C").Insert Shift:=xlToRight
F.Range("C1:C" & Range("A65536").End(xlUp).Row).Value = ActiveSheet.Name
Next F
End If
Next wb
End Sub