How could I know all the categories from post?

Your problem lies in this piece of code

$categoriaActual = get_the_category($post->ID);                
$idCategoriaActual = $categoriaActual[0]->term_id;

The first line gets the categories that belongs to the post in an array, that is fine (Just one note, when inside the loop, you don’t need to pass the post ID, that is done by default). Your second line of code only displays the first category in the returned array. $categoriaActual[0] means that you are only returning the first element in the array, ie, the first category in the array

You can have a look at the example from the codex page of get_the_category. You can just replace the two lines I’ve highlighted in my answer with the code below. Modify and use as needed

$categories = get_the_category();
$separator=" ";
$output="";
if($categories){
    foreach($categories as $category) {
        $output .= '<a href="'.get_category_link( $category ).'" title="' . esc_attr( sprintf( __( "View all posts in %s" ), $category->name ) ) . '">'.$category->cat_name.'</a>'.$separator;
    }
echo trim($output, $separator);
}