The password will take effect when one of ProtectWorkbookWindows and ProtectWorkBookStructure property is true. If one or both ProtectWorkbookWindows and ProtectWorkBookStructure property are set to true, Workbook.Save method will be invoked.At this time, ProtectWorkbookPassword validity will be checked.
If file format is Xls95/Xls97Plus, InvalidPasswordExpection will be thrown out if ProtectWorkbookPassword contains more than 15 characters.If file format is Xlsx, InvalidPasswordExpection will be thrown out if ProtectWorkbookPassword contains more than 255 characters.