Function to use PDF thumbnails within Toolset

function getPDFimg($atts) {

             extract( shortcode_atts( array(
            'size'=>'full',
        ), $atts ) );

            $image_url = str_replace(".pdf", "-pdf.jpg", types_render_field( "document-file", array('output'=> 'raw'))); // publication_document = your field name
            $dirname = str_replace('.jpg','',str_replace(home_url('/'),'',$image_url));
            $images = glob($dirname."*.jpg");
            if(isset($images[0])){
                        $small_image = home_url('/').$images[0];
            }
            if(isset($images[1])) {
                        $medium_image = home_url('/').$images[1];
            }
            if(isset($images[2])) {
                        $large_image = home_url('/').$images[2];
            }

            switch($size) {
                        case 'small':
                                    if(isset($small_image) && $small_image != '' ) {
                                                $image_src = $small_image;
                                    }
                                    else{
                                                $image_src = $image_url;
                                    }
                        break;

                        case 'medium':
                                    if(isset($medium_image) && $medium_image != '' ) {
                                                $image_src = $medium_image;
                                    }
                                    else{
                                                $image_src = $image_url;
                                    }
                        break;

                        case 'large':
                                    if(isset($large_image) && $large_image != '' ) {
                                                $image_src = $large_image;
                                    }
                                    else{
                                                $image_src = $image_url;
                                    }
                        break;

                        default:
                                    $image_src = $image_url;

            }

    return '<img src=' .$image_src  . ' class="pubdoc-pdf-image"> ';
}

add_shortcode('getpublicationpdfimg', 'getPDFimg');