The file format and extension dont match | Microsoft Excel | FIX TUTORIAL 

This Microsoft Excel notification appears when opening a Microsoft Excel file. Selecting Yes at the notification resumes launching the Microsoft Excel file but does not fix the issue.
Registry Path: HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\15.0\Excel\Security
Open the Run window, by pressing the Windows key + R
Type regedit, then select OK
In the Registry Editor window, go to the Registry Path mentioned above
Right-click in the blank section on the right, then select New
Select DWORD (32bit) Value
Name the new entry: ExtensionHardening
Set the Hexadecimal value to 0
Voila. Your files should now launch without this error
To use in Command Prompt batch file:
(Copy the text below and paste into notepad, save the notepad .txt file as .bat)
REG ADD "HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\15.0\Excel\Security" /v "ExtensionHardening" /t REG_DWORD /d 0
Please leave a comment if you were unable to resolve your issue using this method.