using Infragistics.Documents.Excel;
...
// Load workbook with data
Workbook workbook1 = Workbook.Load(inputStream);
In addition to creating Microsoft® Excel® workbooks, the Infragistics Excel Engine can also read them. You can load an Excel workbook by invoking the Workbook's static Load method and provide an input stream to an Excel workbook content source. As a result a Workbook object is created and its object model is populated with all the features supported by the Infragistics Excel Engine. Cell values and formats, as well as workbook and worksheet options are all accessible and modifiable from the parsed workbook.
The following example code demonstrates how to load an existing workbook.
In C#:
using Infragistics.Documents.Excel;
...
// Load workbook with data
Workbook workbook1 = Workbook.Load(inputStream);