Convert XLTX To SPREADSHEETML Online for Free. Free Online XLTX To SPREADSHEETML Converter. C# XLTX To SPREADSHEETML. XLTX To SPREADSHEETML via C#....PDF MD HTML TXT MHTML ODT OTT XPS PNG BMP EMF GIF SVG TIFF JPG...Cells; var workbook = new Workbook( "Input.xlsx" ); workbook.Save(...