public void InitializeFrom(string templatePath, IWorksheetWriter worksheetWriter) { if (worksheetWriter == null) { throw new ArgumentNullException("worksheetWriter"); } byte[] byteArray = File.ReadAllBytes(templatePath); MemoryStream stream = new MemoryStream(byteArray); using (SpreadsheetDocument spreadsheetDoc = SpreadsheetDocument.Open(stream, true)) { // Change from template type to workbook type spreadsheetDoc.ChangeDocumentType(SpreadsheetDocumentType.Workbook); WorksheetPart worksheetPart = ExcelUtility.GetWorksheetPartByName(spreadsheetDoc, worksheetWriter.SheetName); if (worksheetPart != null) { worksheetWriter.CreateHeader(worksheetPart); } } FileContentStream = stream; }