.docx file extension

Problems to open a file extension docx?
First what is it, what does the docx mean?
It is a Word processing format introduced with Microsoft Word 2007 (it belongs to Office 12); it is based on Open XML and uses ZIP compression for smaller file sizes. It could be compatible with Microsoft Office 2000, Office XP, and Office 2003 if the Microsoft Office Compatibility Pack (FileFormatConverters.exe) is installed.
If any doubt you can check the Microsoft support page.
With the appropriate software you can convert a file extension docx document into a Word document.
The programs that can open a file extension docx can be for a MAC os: Microsoft Word 2008, Apple Pages, Panergy docXConverter; for a Windows os: Microsoft Word 2007, Microsoft Word with Compatibility Pack, Panergy docXConverter, OxygenOffice Professional, OpenOffice.org with Odf-Converter, NativeWinds Docx2Rtf; and for a Linux os: OxygenOffice Professional, OpenOffice.org with Odf-Converter.