// Get the input collection
    DataTable dt = CollectionIn;

    // Loop through each row in the input collection
    for (int i = 0; i < CollectionIn.Rows.Count; i++)
    {
        // Get the values of the two columns
         string UniqueIDValue = CollectionIn.Rows[i]["Unique ID"].ToString();
         string PDFInvoiceNumberValue = CollectionIn.Rows[i]["PDF Invoice Number"].ToString();

        // Check if the value is a duplicate
        for (int j = i + 1; j < CollectionIn.Rows.Count; j++)
        {
            if (UniqueIDValue == CollectionIn.Rows[j]["Unique ID"].ToString() && PDFInvoiceNumberValue  == CollectionIn.Rows[j]["PDF Invoice Number"].ToString())
            {
                
                CollectionIn.Rows[i]["Unique ID"] = UniqueIDValue + (char)('A' + j - i - 1);
                CollectionIn.Rows[i]["PDF Invoice Number"] = PDFInvoiceNumberValue + (char)('A' + j - i - 1);
                CollectionIn.Rows[j]["Unique ID"] = UniqueIDValue + (char)('A' + j - i);
                CollectionIn.Rows[j]["PDF Invoice Number"] = PDFInvoiceNumberValue + (char)('A' + j - i);
            }
        }
    }
	
	   
Result = dt;