Convert RenderTexture to Texture2D

I need to save a RenderTexture object to a .png file that will then be used as a texture to wrap about a 3D object. My problem is right now I can't save a RenderTexture object using EncodeToPNG() because RenderTexture doesn't include that method. How can I convert a RenderTexture object into a Texture2D object? Thank you!

// Saves texture as PNG file.
using UnityEngine;
using System.Collections;
using System.IO;

public class SaveTexture : MonoBehaviour {

    public RenderTexture tex;

    // Save Texture as PNG
    void SaveTexturePNG()
    {
        // Encode texture into PNG
        byte[] bytes = tex.EncodeToPNG();
        Object.Destroy(tex);

        // For testing purposes, also write to a file in the project folder
        File.WriteAllBytes(Application.dataPath + "/../SavedScreen.png", bytes);
    }
}