Convert XLS to XLSX in C#

To convert XLS to XLSX in C# - simply load an XLS Excel workbook with IronXL, and then save with the ".xlsx" file extension.

Note that images, charts, split panes, freezing panes will not always be copied between XLS and XLSX formats.

IronXL can convert between XLS, XLSX, XLSM, CSV, TSV, JSON, XML files simply by loading and saving with the relevant file extensions.