I have used this method on .xlsx files I downloaded from
Excel 2010, 2013, etc. - Password Removal
- Create backup of password-protected excel file.
- Change the file extension from .xlsx to .zip
- Now extract the whole content of zip file.
- Search for xml format of targeted sheet. You will find it in ‘xl -> worksheets’ directory.
- Open the xml file of targeted sheet in xml editor.
- Now search for ‘sheetProtection’ word in that xml file and remove it.
- Save this edited xml file and replace it with old xml file in zip files.
- Now change the extension from .zip to .xlsx.