Convert SPREADSHEETML To XLTX Online for Free. Free Online SPREADSHEETML To XLTX Converter. C# SPREADSHEETML To XLTX. SPREADSHEETML To XLTX via C#....files as images, PDF, HTML, ODS, CSV, SVG, JSON, WORD, PPT and more...Cells for .NET DLL in your project. Other Supported Conversions...