open the file for reading
line by line, append each line to a variable
close the file
spawn a control with that variable as the contents

string[] ass_variable = File.ReadAllLines(ass_path_of_txtfile);

using (FileStream stream = new FileStream("file.txt", FileMode.Open, FileAccess.Read))
using (StreamReader reader = new StreamReader(stream))
      {
          string line = string.Empty;
          while ((line = reader.ReadLine()) != null)
          {
              Console.WriteLine(line);
          }
      }