Well, we did evaluate this already. I am afraid, it’s not allowed to unprotect a workbook/worksheet without correct password in MS Excel. Aspose.Cells works the same way and follows MS Excel standards, so we will not support this feature.
Please note, it is also not possible for Aspose.Cells either. Just create an Excel file with Microsoft Excel and then password protect it. Then rename your Excel file to something like abc.zip and then try to extract its contents with WinRAR tool and you will see, zip file is damaged. It is because when you password protect the Excel file, then Microsoft Excel uses an Encryption Algorithm most probably (AES i.e. Advanced Encryption Standard) to encrypt its contents.
Microsoft Excel itself cannot decrypt the Excel file without password. No application can decrypt it without password because Excel file contents are encrypted with AES.