ClosedXML のサンプル

ExcelSummarizer.cs

static void Main(string[] args)
{
	var path = ConfigurationManager.AppSettings["InputPath"];
	var outPath = ConfigurationManager.AppSettings["OutputPath"];
	var files = Directory.GetFiles(path);
	var allRows = new List<AlertModel>();

	foreach (var file in files)
	{
		using (var book = new XLWorkbook(file, XLEventTracking.Disabled))
		{
			var sheet = book.Worksheet(ConfigurationManager.AppSettings["SheetName"]);
			var lastRowNumber = sheet.LastRowUsed().RowNumber();

			foreach (var row in sheet.Range("A:R").Rows(9, lastRowNumber)
			{
				allRows.Add(new Model
				{
					DateTime = row.Cell(1).Value.ToString(),
					Description = row.Cell(2).Value.ToString(),
				});
			}
		}
	}

	using (var outbook = new XLWorkbook())
	{
		var sheet = outbook.Worksheets.Add("一覧");
		sheet.Cell(1, 1).Value = allRows;
		outbook.SaveAs(Path.Combine(outPath, "all.xlsx"));
	}
}

Model.cs

public class Model
{
  public string DateTime { get; set; }
  public string Description { get; set; }
}