Workbook.ExportToHtmlAsync(Stream, Int32) Method
Asynchronously exports the specified range to the specified stream in HTML format.
A Stream object to which the created HTML file should be sent.
An integer value that is the index of the worksheet to be exported to HTML.
An Task object representing an asynchronous export operation.
Take into account the following when you call this method:
The events fired by this method call may occur in a different thread than the target operation.
The operation is not thread safe (the document should not be accessed simultaneously by different threads). Wait until the operation is completed before you continue to work with the document (for example, use the
Calculate Formulas Before Export
The default calculation mode for a Workbook is Manual. This mode implies that the Spreadsheet does not recalculate formulas before it generates an HTML file. Call the Workbook.Calculate or Workbook.CalculateFull method to calculate all formulas in the workbook before you export it to HTML.