I just tried to use Aspose.Excel to copy an Excel file without changing anything. The new copied file has larger size than the original one. Excel 2000 was used to create the original file. I saved the new copied file under Excel 2000 type. The difference in size is not much, however if someone else looks at the two files sit next to next, he/she could not tell one file is just a copy of another because their sizes are different. I don’t know if anything you can do to improve this. At least make the size smaller/equal, not bigger.