TextLoader.cs

using UnityEngine;
using System.Collections;
using UnityEngine.UI;
using UnityEngine.Networking;

public class TextLoader : MonoBehaviour
{
    public string url = "http://www.dominio.com/arquivo.txt";
    public Text textUI;

    public bool isLoaded = false;

    // Use this for initialization
    void Start()
    {
        StartCoroutine(LoadText());
    }

    public IEnumerator LoadText()
    {
        using (UnityWebRequest www = UnityWebRequest.Get(url))
        {
            yield return www.Send();

            if (www.isNetworkError || www.isHttpError)
            {
                Debug.Log(www.error);
            }
            else
            {
                Debug.Log("www returned");
                textUI.text = www.downloadHandler.text;
                isLoaded = true;
                Debug.Log(www.downloadHandler.text);
            }
        }
    }
}