If you came across an excel sheet asking for password for allowing to make any changes into it, you may want to unprotect it.
All we need to do is to edit the xml file which comes intrinsically packaged with Excel 2007 or 2010. But what about Excel 2003? For that, open the Excel 2003 file within Excel 2007, save it as xlsx file. So, keep in mind all the Excel files below 2007 version, you need to convert them as Excel 2007 with extension .xlsx.
Now here are the steps for doing that:
1. Open the Excel 2003 file (e.g. Secret.xlsx) and save it as .xlsx (Excel 2007) format. If you already have Excel 2007 file, then no need for any conversion.
2. Now change the extension of the above file to .zip and extract the zipped file. Browse through the file in the extracted folder and go to:
3. Now open the sheet/ sheets you want to remove protection in any xml editor. Look for keywords such as 'sheetProtection' or 'workbookProtection' in the xml file.
Remove such lines entirely from the xml files above. Do this for all the sheets you want to remove the protection.
4. Now, copy all these edited and saved xml files to the original zip file under the same path. Now change the extension back to .xlsx from .zip. You are done!