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.

Solution 7: Open MS Excel in Safe Mode Solving the “ Excel cannot open because the file format is not valid ” problem can sometimes be as simple as booting your computer into Safe Mode . This is ...

To fix the Excel file format does not match extension error, trying opening the spreadsheet with the Open and Repair option or changing its file extension.

Excel cannot open file 'file.xlsx' because file... Every now and then, when I try opening an Excel file, I get a message saying that "Excel cannot open the file 'file.xlsx' because the file format or ...

With the Excel extension is not valid error, try starting the app in Safe Mode, repair the workbook or open the file in another program.

"Excel cannot open the file because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file".

Am I forgetting something, which makes the file unreadable? Error message: Excel cannot be open the file 'filename.xlsx' because the file format or file extension is not valid.

This is not a valid bitmap file, or its format is not currently supported. However, the same files can be opened using apps like GIMP, Photoshop, Paint 3D, IrfanView, Paint.net, etc.