On the Microsoft support forum, some Excel users have discussed an error message that states: The file format and extension of ‘file.xls’ don’t match. The file could be corrupted or unsafe. Unless you trust its source, don’t open it. Do you want to open it anyway?

Users can then select to open the Excel file. However, users have said that their spreadsheet files have lost all their data when they click Yes to open. If you need to fix that same error, check out some of the resolutions for it below.


What can I do if Excel file format and extension don’t match?

1. Change the file’s extension

  1. Some users have fixed the issue by manually changing the file’s extension to various standard Excel file formats until they get the right one. Click the File Explorer button on Windows 10’s taskbar.
  2. Select the File name extensions option on the View tab.
    File name extensions check box excel file format does not match extension
  3. Open the folder that includes the Excel file the error arises for.
  4. Right-click the file and select the Rename option.
  5. Then edit the extension at the end of the file to. xls, .xlsx, or .xlsm. Try opening the Excel spreadsheet with each of those alternative file formats.

2. Select the Open and Repair option

  1. The Excel file might be corrupted, and you can fix it with the Open and Repair option. First, open Excel’s window.
  2. Select the File tab.
  3. Click Open to the open the window shown directly below.Open window excel file format does not match extension
  4. Select the file the issue arises for.
  5. Then click the arrow on the Open button. Select the Open and Repair option.Open and Repair option excel file format does not match extension
  6. Select the Repair option.
  7. If the Repair option doesn’t fix the issue, repeat the above steps and click the Extract Data button. Then you can click Convert to Values to extract data from the sheet.

3. Unblock the Excel file

  1. Some users have confirmed they’ve fixed the file format does not match extension error by unblocking the file. To do so, open File Explorer.
  2. Open the folder path that includes the Excel spreadsheet file which needs fixing.
  3. Right-click the Excel file to select the Properties option.
  4. Select the General tab on that window.
  5. Click the Unblock option. Note that option will only be visible for files that came from another source, such as email attachments.Unblock option excel file format does not match extension
  6. Press the Apply button.
  7. Click exit to close the window.

4. Turn off Protected View

  1. Turning Excel’s Protected View off might also resolve the file format does not match error. Click Excel’s File tab.
  2. Click Options to open a window like the one shown directly below.Excel Options excel file format does not match extension
  3. Click the Trust Center tab on the left of the window.
  4. Press the Trust Center Settings button.Trust Center excel file format does not match extension
  5. Then click Protected View on the Trust Center window.
    Protected View options excel file format does not match extension
  6. Deselect all three Enable Protected View settings there.
  7. Click the OK option on the Trust Center window.
  8. Then click OK again to exit the other window.

5. Open the file in LibreOffice Calc

You can also try opening the Excel file the error arises for in LibreOffice Calc. That’s a freeware spreadsheet application you can add to Windows by clicking Download on the Download LibreOffice page. Then install Calc’s office suite with the downloaded setup wizard.
LibreOffice Calc excel file format does not match extension

When you try opening the file in LibreOffice Calc, the application might ask you to select an appropriate format. Select alternative formats until you get the file opened. Thereafter, you can copy and paste all the data in the spreadsheet into a blank Excel sheet with the Ctrl + C and Ctrl + V keyboard shortcuts.


Those are some of the confirmed resolutions that users have fixed Excel’s file format does not match extension error with.

If the file the issue arises for is not from a trusted source, however, do not select to open it. Instead, scan the file with antivirus utility before trying to open it.

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