Is important to import a file from your asset folder for input with the assetManager. Nothing else works at me. I try a script objLoader to import a cube.obj with the try:

        try { //try to open file
            reader = new BufferedReader(new InputStreamReader(new FileInputStream(fileName)));
        }

 this sucks completely.

Now i do that:

Open an asset using ACCESS_STREAMING mode. This provides access to files that have been bundled with an application as assets -- that is, files placed in to the "assets" directory.

AssetManager assetManager = getAssets();
              
        // To load text file
        InputStream input;
        try {
            input = assetManager.open("cube.obj");
            
             int size = input.available();
             byte[] buffer = new byte[size];
             input.read(buffer);
             input.close();

             // byte buffer into a string
             String text = new String(buffer);
            
             txtContent.setText(text);
        }

 Thats is it.