// Path of input XLS and output XLSX files.
intrusive_ptr<Aspose::Cells::System::String> inputXLSFile = new Aspose::Cells::System::String("D:/Download/SampleConvertMicrosoftExcelXLSToXLSX.xls");
intrusive_ptr<Aspose::Cells::System::String> outputXLSXFile = new Aspose::Cells::System::String("D:/Download/OutputConvertMicrosoftExcelXLSToXLSX.xlsx");

// Specify load options Excel97To2003 i.e. XLS format.
intrusive_ptr<Aspose::Cells::ILoadOptions> opts = Aspose::Cells::Factory::CreateILoadOptions(Aspose::Cells::LoadFormat_Excel97To2003);

// Load the input XLS file inside the Aspose.Cells workbook object.
intrusive_ptr<Aspose::Cells::IWorkbook> wb = Aspose::Cells::Factory::CreateIWorkbook(inputXLSFile, opts);

// Save the workbook as output XLSX file.
wb->Save(outputXLSXFile, Aspose::Cells::SaveFormat::SaveFormat_Xlsx);