I have a program that combines three text files and put them all into one and sorts them all out alphabetically. I was wondering how I could possibly put this onto an excel spreadsheet without downloading and using the excellibrary (if that's possible). 

Heres my code that combines all three files if that helps.

```
    private void button1_Click(object sender, EventArgs e) // merge files button
    {

        System.IO.StreamWriter output = new System.IO.StreamWriter("OUTPUT.txt");

        String[] parts = new String[1000];
        String[] parts2 = new String[1000];

        parts = File.ReadAllLines(textBox1.Text);       //gets filepath from top textbox
        parts2 = File.ReadAllLines(textBox2.Text);      //gets filepath from middle textbox

        String[] head = File.ReadAllLines(headingFileBox.Text); //header file array

        //merging the two files onto one list, there is no need to merge the header file because no math is being
        //computed on it
        var list = new List<String>();
        list.AddRange(parts);
        list.AddRange(parts2);

        //foreach loop to write the header file into the output file
        foreach (string h in head)
        {
            output.WriteLine(h);
        }
        //prints 3 blank lines for spaces
        output.WriteLine();
        output.WriteLine();
        output.WriteLine();

        String[] partsComb = list.ToArray(); // string array that takes in the list
        Array.Sort(partsComb);
        //foreach loop to combine files and sort them by 1st letter
        foreach (string s in partsComb)
        {
            partsComb.Equals(s);
            output.WriteLine(s);
        }
        output.Close();
    }

```

Any help would be much appreciated.