Find window handle in WPF

About the window handles thing, Bharat Kumar has answered it as I don't have much information about it.

However to read the Excel content, you need to use the Interop.Excel, you may also need to use Add-in.

Add this namespace :

Using xl = Microsoft.Office.Interop.Excel;

private xl.Application xlApp;

//Do this in your Ribbon_Load event :
xlApp = Globals.ThisAddin.Application;

xl.WorkBook workbook = xlApp.ActiveWorkbook;  //Get the active workbook object
xl.WorkSheet worksheet = workbook.ActiveSheet;  //Get the active worksheet object
xl.Range usedRange = worksheet.UsedRange;  //This will return the whole range where you data is used in it

String value;

// Loop through the range to get data of each cell
foreach(xl.Range rng in usedRange.Cells) 
{
 value = rng.Value;
}

Let me know if you have any questions.