This C# example showcases how to open an existing MS excel workbook and insert text into a specified cell using the FileFormat.Cells library.

open-existing-workbook.cs

using FileFormat.Cells

string filePath = "Z:\\Downloads\\testFile1.xlsx";

// Load the workbook from the specified file path
using (Workbook wb = new Workbook(filePath))
{
    // Access the first worksheet in the workbook
    Worksheet firstSheet = wb.Worksheets[0];

    // Define the cellReference
    string cellReference = "B10";
    Cell cell = firstSheet.Cells[cellReference];
    
    // Insert the actual value to the cell.
    cell.PutValue("randomValue"); 

    wb.Save(filePath);
}