If you cannot open an Excel file and see Excel cannot open the file because the file format or extension is not valid error, see this post.

How to Open an XLS File in Excel. XLS files are Excel workbook files created in Excel 97 or Excel 2003. The 2007, 2010 and 2013 versions of the program use the XLSX format by default to save ...

Taking XLSM File Precautions Before trying to open an XLSM file, Kaspersky warns that some macros in these files can be malicious, especially if you receive your spreadsheet through a random email.

How to open a .csv file in Excel Opening a .csv file is as easy as opening a .txt file, and usually, you won’t have to clean up the data before doing so because the save task inserts the delimiter.

Microsoft Word can accommodate a surprising number of file formats, and even take in Excel and PowerPoint data, though it might look funny. Here's how.