An XLSX file is an Excel spreadsheet that was created with Microsoft Office. MS Office includes a new XML-based file format — files saved in this new format have an “x” appended to the file extension.
A friend sent me a .xlsx file. What is it, and how do I open it?
Word Documents are now .docx files, Excel spreadsheets are now .xlsx files, and PowerPoint files are now .pptx files.
If you do not own Microsoft Office, you can use the Excel Viewer from Microsoft to look at the .xlsx file. The latest version of the Excel Viewer software is compatible with the latest file formats from Microsoft Office 2007.
If you have Microsoft Office XP or Office 2003, you can open .xlsx files by installing the Microsoft Office Compatibility Pack.