Invalid formula handling

Refer to the following example code to see how to use **XlsxOpenOptions.InvalidFormulaHandling** when opening an Excel file. Available values: - **Throw** (default): Throws an exception if an invalid formula is found. - **Discard**: Discards the invalid formula text and cached value. - **DiscardFormulaOnly**: Discards only the invalid formula text and keeps the cached value. - **Preserve**: Preserves the invalid formula text and cached value. This demo opens the workbook with **Preserve**.