Search by Post ID and display content of the post in search result

Put any of the filters in the functions.php

Using pre get posts

// Filter the search page
add_filter('pre_get_posts', 'search_pre_get_posts');

function search_pre_get_posts($query)
{
    // Verify that we are on the search page that that this came from the event search form
    if($query->query_vars['s'] != '' && is_search())
    {
        // If "s" is a positive integer, assume post id search and change the search variables
        if(absint($query->query_vars['s']))
        {
            // Set the post id value
            $query->set('p', $query->query_vars['s']);

            // Reset the search value
            //$query->set('s', '');
        }
    }
}

Using posts where query

add_filter('posts_where', 'posts_where');
    function posts_where($where)
        {

            $s = $_GET['s'];

            if(!empty($s))
            {
              if(is_numeric($s))
              {
                global $wpdb;

                $where = str_replace('(' . $wpdb->posts . '.post_title LIKE', '(' . $wpdb->posts . '.ID = ' . $s . ') OR (' . $wpdb->posts . '.post_title LIKE', $where);
              }
              elseif(preg_match("/^(\d+)(,\s*\d+)*\$/", $s)) // string of post IDs
              {
                global $wpdb;

                $where = str_replace('(' . $wpdb->posts . '.post_title LIKE', '(' . $wpdb->posts . '.ID in (' . $s . ')) OR (' . $wpdb->posts . '.post_title LIKE', $where);
              }
            }


          return $where;
        }

Use any one functions as your need. The first function gives you exact search using search id. ex: 1 gives you 1 id’s post only.

Now how to show posts all value I am given you hints.

Edit your search.php or add search.php in your theme. Basically every theme has search.php, so you just need to modify a little bit.

I am giving you some example code for search.php. you will modify it as your need.

<?php
if ( have_posts() ) :
while ( have_posts() ) :  the_post();
$post_id = get_the_ID();
$id = get_post_thumbnail_id($post_id);
$image = wp_get_attachment_image_url($id,'full');
?>
// Print The title
<?php echo get_the_title($post_id); ?>
//print full content of the post
<?php echo get_the_content(); ?>
//print the excert
<?php print get_the_excerpt($post_id); ?>
// print the image  
<img src="https://wordpress.stackexchange.com/questions/262104/<?php echo $image; ?>" class="attachment-portfolio-three size-portfolio-three wp-post-image" alt="">
// suppose custom field
<a href="<?php echo get_the_permalink($post_id); ?>">
                          <?php echo get_post_meta($post_id,'custom_field_1',true);?>
                        </a>
// suppose custom field 2
<a href="<?php echo get_the_permalink($post_id); ?>">
                          <?php echo get_post_meta($post_id,'custom_field_2',true);?>
                        </a>
// suppose custom field  3                          
<a href="<?php echo get_the_permalink($post_id); ?>">
                          <?php echo get_post_meta($post_id,'custom_field_2',true);?>
                        </a>                                                        
<?php endwhile;?>
<?php wp_reset_query();
// print pagination and also its arg if you use my code.
paginate_links($args); 
else :
?>
<p><?php _e( 'Sorry, but nothing matched your search terms. Please try again with some different keywords.', 'twentyseventeen' ); ?></p>
  <?php
    get_search_form();

endif;
?>