The custom post type do not support the category tags and authors here is how you can have it done

Following is a part of hook used to add support

function add_wp_taxonomy_to_cpt() {
	//Replace post_type with actual CPT slug
	register_taxonomy_for_object_type( 'category', 'articles' ); 
	register_taxonomy_for_object_type( 'post_tag', 'articles' );
	add_post_type_support( 'articles', 'author' );
}
add_action( 'init', 'add_wp_taxonomy_to_cpt' );


function my_pre_get_posts($q) {
	if( (is_category() || is_tag() || is_author() ) && $q->is_main_query() ) {
		$pt = get_query_var('post_type');
		if(!$pt)
			$pt = array('nav_menu_item', 'articles'); // don't forget nav_menu_item to allow menus to work!
		$q->set('post_type', $pt);		
    }
}
add_filter('pre_get_posts', 'my_pre_get_posts');

Following is part of code to be used to declare support for category tags and author while creating a custom post type

// Register Custom Post Type
function custom_articles_type() {

	$labels = array(
		'name'                  => _x( 'Articles', 'Post Type General Name', 'text_domain' ),
		'singular_name'         => _x( 'Articles', 'Post Type Singular Name', 'text_domain' ),
		'menu_name'             => __( 'Articles', 'text_domain' ),
		'name_admin_bar'        => __( 'Articles', 'text_domain' ),
		'archives'              => __( 'Articles Archives', 'text_domain' ),
		'attributes'            => __( 'Articles Attributes', 'text_domain' ),
		'parent_item_colon'     => __( 'Parent Articles:', 'text_domain' ),
		'all_items'             => __( 'All Articles', 'text_domain' ),
		'add_new_item'          => __( 'Add New Article', 'text_domain' ),
		'add_new'               => __( 'Add Article', 'text_domain' ),
		'new_item'              => __( 'New Article', 'text_domain' ),
		'edit_item'             => __( 'Edit Article', 'text_domain' ),
		'update_item'           => __( 'Update Article', 'text_domain' ),
		'view_item'             => __( 'View Article', 'text_domain' ),
		'view_items'            => __( 'View Article', 'text_domain' ),
		'search_items'          => __( 'Search Article', 'text_domain' ),
		'not_found'             => __( 'Not found', 'text_domain' ),
		'not_found_in_trash'    => __( 'Not found in Trash', 'text_domain' ),
		'featured_image'        => __( 'Featured Image', 'text_domain' ),
		'set_featured_image'    => __( 'Set featured image', 'text_domain' ),
		'remove_featured_image' => __( 'Remove featured image', 'text_domain' ),
		'use_featured_image'    => __( 'Use as featured image', 'text_domain' ),
		'insert_into_item'      => __( 'Insert into item', 'text_domain' ),
		'uploaded_to_this_item' => __( 'Uploaded to this item', 'text_domain' ),
		'items_list'            => __( 'Items list', 'text_domain' ),
		'items_list_navigation' => __( 'Items list navigation', 'text_domain' ),
		'filter_items_list'     => __( 'Filter items list', 'text_domain' ),
	);
	$args = array(
		'label'                 => __( 'Articles', 'text_domain' ),
		'description'           => __( 'Articles', 'text_domain' ),
		'labels'                => $labels,
		'supports'              => array( 'title', 'editor', 'author', 'thumbnail', 'comments', 'revisions', 'custom-fields', 'page-attributes', 'post-formats' ),
		'taxonomies'            => array( 'category','post_tag', ),
		'hierarchical'          => false,
		'public'                => true,
		'show_ui'               => true,
		'show_in_menu'          => true,
		'menu_position'         => 5,
		'show_in_admin_bar'     => true,
		'show_in_nav_menus'     => true,
		'can_export'            => true,
		'has_archive'           => true,
		'exclude_from_search'   => false,
		'publicly_queryable'    => true,
		'query_var'  			=> true,
		'capability_type'       => 'page',
	);
	register_post_type( 'articles', $args );

}
add_action( 'init', 'custom_articles_type', 0 );