Create a custom widget and call it by using shortcode in wordpress

Copy code in functions.php

<?php
function widget($atts) {
    
    global $wp_widget_factory;
    
    extract(shortcode_atts(array(
        'widget_name' => FALSE
    ), $atts));
    
    $widget_name = wp_specialchars($widget_name);
    
    if (!is_a($wp_widget_factory->widgets[$widget_name], 'WP_Widget')):
        $wp_class = 'WP_Widget_'.ucwords(strtolower($class));
        
        if (!is_a($wp_widget_factory->widgets[$wp_class], 'WP_Widget')):
            return '
'.sprintf(__("%s: Widget class not found. Make sure this widget exists and the class name is correct"),''.$class.'').'
';
        else:
            $class = $wp_class;
        endif;
    endif;
    
    ob_start();
    the_widget($widget_name, $instance, array('widget_id'=>'arbitrary-instance-'.$id,
        'before_widget' => '',
        'after_widget' => '',
        'before_title' => '',
        'after_title' => ''
    ));
    $output = ob_get_contents();
    ob_end_clean();
    return $output;
    
}
add_shortcode('widget','widget'); 
?>

Usage
Now in Post/Page content, you can use the widget just by referencing it by name:
[widget widget_name="Your_Custom_Widget"]
enjoy!!