如何在不安装c#的情况下创建带有密码保护的Excel 2003 (.XLS)文件?

In C#, how can I create a PASSWORD PROTECTED (user has to enter password to OPEN the file at all) .XLS file without having Excel installed (therefore not Interop)? NPOI and ExcelLibrary look promising (because they are free!), but I cannot seem to find anywhere whether or not they actually support password protection. I cannot use EPPlus since it only deals with .XSLX file types, not my required .XLS.In C#, how can I create a PASSWORD PROTECTED (u