The easist way to work out code with Excel is to Start the Macro Recorder, do the steps:
1. Select all cells (Top left corner between the row and column headers)
2. Copy
3. Switch workbooks
4: Select all cells
5: Paste
Now stop the recording, go to the Macro Editor, and view the VBA code generated. It is very close to the methods that you need to use in your C# code.
UPDATE
I found some time to try it out and found that for what you want to do it was not very helpful.
After a little experimenting I came up with the following:
using Microsoft.Office.Interop.Excel;
using _Excel = Microsoft.Office.Interop.Excel;
string safeExcelFilePath = @"[directory of the excel workbooks]";
string excelFile1 = Path.Combine(safeExcelFilePath, "Book1.xlsx");
string excelFile2 = Path.Combine(safeExcelFilePath, "Book2.xlsx");
_Application _excel = new _Excel.Application();
_excel.DisplayAlerts = false;
Workbook workbook1 = _excel.Workbooks.Open(excelFile1);
Workbook workbook2 = _excel.Workbooks.Open(excelFile2);
Worksheet worksheet1 = workbook1.Worksheets["Sheet1"];
Worksheet worksheet2 = workbook2.Worksheets["Sheet1"];
worksheet2.UsedRange.Delete(Type.Missing);
worksheet1.UsedRange.Copy(Type.Missing);
worksheet2.UsedRange.PasteSpecial(
XlPasteType.xlPasteAll,
XlPasteSpecialOperation.xlPasteSpecialOperationNone,
Type.Missing, Type.Missing);
workbook2.SaveAs(
Filename: excelFile2,
AccessMode: XlSaveAsAccessMode.xlNoChange);
workbook2.Close();
workbook1.Close();
_excel.Quit();