The process cannot acces the file because is being used by another prc

int i, j, k, l;
string sourcefile = "C:\\Users\\K90009861\\Downloads\\newfisier.txt";
Microsoft.Office.Interop.Excel.Application xlApp;
Microsoft.Office.Interop.Excel.Workbook xlWorkBook;
Microsoft.Office.Interop.Excel._Worksheet xlWorkSheet;
System.Reflection.Missing value = System.Reflection.Missing.Value;
object Value = value;
string[] lines, cells;
lines = File.ReadAllLines(sourcefile);