How to update data on opened Excel file with C# application?

I'd like to start a C# application from Excel 2007 which read and write data in the same opened XLS file. In this XLS file, I have input data sheets, a button to start my C# application (process or dll) and some sheets to collect results from my C# application in dedicated output sheets.

The user open the XLS file, fill data sheet, and then start on 'compute' button to start my C# application has to read the current XLS file in which it will read data, do some computation, and the write data in new sheet in my same opened Excel file.

Is it possible to do that without intermediate files like .csv or .txt file ?

Which library should I use in C# to do that ?

Thanks