.xlsx file is a Excel 2007 workbook.
Currently only Excel 2007 and Excel 2010 use this file type. Previous Excel
versions use .xls file type.
To break password protected Excel 2007 workbook (.xlsx file) you can use
Excel
Password program. Excel
Password recovers all Excel password types and supports all
Excel versions (including Excel 2007).
Possible password types:
Password to open
Password to modify
Workbook protection password
Worksheet/ and cell passwords
Excel document may contain a VBA project inside. To
recover password-protected VBA project you should use
VBA Password program.