Display pages from specific page template

Use get_post_field('post_content', $product_page->ID ) to get the content outside loop.

<?php
$product_pages_args = array(
    'meta_key' => '_wp_page_template',
    'meta_value' => 'page_library_html.php'
);
$product_pages = get_pages( $product_pages_args );
?>

<?php
foreach ( $product_pages as $product_page ) {
    echo '<div id="posts" class="flex_100">';
    echo '<div id="library_title"><a href="' . get_permalink( $product_page->ID ) . '">' . $product_page->post_title  . '</a></div>';
    echo '<div class="page-content">' . get_post_field('post_content', $product_page->ID ) . '</div></div>';
}
?>