// var lines = File.ReadAllLines("text.txt");
var lines = new string[]
{
"A\tB\tC\tD\tE\t1",
"A\tB\tC\tD\tE\t2",
"A\tB\tC\tD\tE\t3",
"A\tB\tC\tD\tE\t4",
"A\tB\tC\tD\tE\t5",
};
var result = lines.Select(x => x.Split('\t').Last());
foreach (var value in result)
Console.WriteLine(value);