ExcelTemplate is the main class for template-driven document generation. This object opens an ExcelWriter template file, populates it with data from a specified data source, and generates a new Excel workbook. An Excel file uploaded as an ExcelTemplate object is not directly modifiable. ExcelApplication is the main class for pure code-based workbook generation. This class is an engine used to open, create, and write (save or stream to a browser) workbooks. A single instance of ExcelApplication can generate multiple Excel workbooks.