Thanks for your interest in Aspose.Cells.
Yes, it is possible. You can join the two workbooks. Please see the code below, it basically copies all the worksheets from source workbook to destination workbook. You can modify it a little and copy all the source worksheets without deleting the destination workbook sheets.
Let me know if you encounter any problem.
string dirPath = @“F:\Downloads”;
Workbook sourceWorkbook = new Workbook(dirPath + “source.xlsx”);
Workbook destWorkbook = new Workbook(dirPath + “destination.xlsx”);
//You should not delete the existing worksheets though
foreach (Worksheet sourceSheet in sourceWorkbook.Worksheets)
destWorkbook.Worksheets[destWorkbook.Worksheets.Count - 1].Copy(sourceSheet);
destWorkbook.Save(dirPath + @“destOutput.xlsx”, SaveFormat.Xlsx);