What are .pptx .xlsx .docx files ? These are the files created by Office 2007, Up to office 2003 the it was .xls .ppt and .doc Most off them started working in Office 2007. If you create and just save a file from Office 2007, users with previous versions cant open this file.
In this case. When you save a file do “Save as” and select option “ **** 97-2003 Document” from the “file menu” Then the saved file will be compactable for the entire previous versions But what will you do when you get a file with these extensions? Don’t worry! Microsoft released a tool to named “Microsoft Office Compatibility Pack” Using this tool you can convert office 2007 files to the compactable file format for older versions
You can download it from here