Gembox.spreadsheet.dll -

workbook.Save("Report.xlsx"); For truly massive files (500k+ rows), use the LoadOptions to stream data:

var workbook = new ExcelFile(); var worksheet = workbook.Worksheets.Add("Sales Report"); gembox.spreadsheet.dll

A unique feature of this DLL is direct HTML rendering: workbook

// Style a header var headerStyle = new CellStyle For truly massive files (500k+ rows)

var worksheet = reader.Worksheets[0]; foreach (var row in worksheet.Rows) // Process row by row without holding entire file in RAM Console.WriteLine(row.Cells[0].Value);

using (var reader = ExcelFile.LoadXlsx("hugefile.xlsx", new XlsxLoadOptions ReadDataOnly = true ))