我学到的是，屏幕截图方法实际上是不可能的。因此，我所做的是使用这里使用FPDF规定的方法：https://wordpress.org/support/topic/convert-pdf-file

最后一篇文章很有启发性。这种方法的问题是，它对表单没有条件，因此需要为此添加一些if语句。此外，我正在使用CF7签名插件，因此需要一种处理该图像的方法。我还介绍了一种将PDF转换为BLOB并将其导入DFDB数据库的方法：

function wpcf7_update_email_body($contact_form) {

        if ( $contact_form->id == 77 ) { //Number of the page for the form you are sending a PDF on.
        $submission = WPCF7_Submission::get_instance();
        if ( $submission ) {
            /* DEFINE CONSTANT AND GET FPDF CLASSES */
            define (\'FPDF_PATH\',get_template_directory().\'/fpdf/\'); // MAKE SURE THIS POINTS TO THE DIRECTORY IN YOUR THEME FOLDER THAT HAS FPDF.PHP
            require(FPDF_PATH.\'fpdf.php\');

            $posted_data = $submission->get_posted_data();
            // SAVE FORM FIELD DATA AS VARIABLES
            $name = $posted_data["your-name"];
            $email = $posted_data["your-email"];
            $subject = $posted_data["your-subject"];
            $message = $posted_data["your-message"];
            $signature = $posted_data["signature-113"];

            $pdf = new FPDF();
            $pdf->AddPage();
            $pdf->SetFont(\'Arial\',\'B\',16);
            $pdf->Write(5,$name . "\\n\\n" . $email . "\\n\\n" . $subject . "\\n\\n" . $message . "\\n\\n");
            $pdf->Image($signature,60,30,90,0,\'PNG\');  // The signiture file image
            $pdf->Output(FPDF_PATH.\'test.pdf\', \'F\'); // OUTPUT THE NEW PDF INTO THE SAME DIRECTORY DEFINED ABOVE
        }
    }   
}
add_action(\'wpcf7_before_send_mail\', \'wpcf7_update_email_body\');


function mycustom_wpcf7_mail_components($components = null, $form = null){
    global $wpdb;
    $current_user = wp_get_current_user();
    $username = $current_user->user_login;
    $file_id = array_sum(explode(\' \', microtime()));        

    if ($form->id == 77) {  //Number of the CF7 form (not the page id) you are sending a PDF on.

        $form_id = $form->id;
        $post = get_post($form_id);
        $formtitle = $post->post_title;
        $ip = getenv("REMOTE_ADDR");

        if (empty($components[\'attachments\'])) {
        $filename = \'test.pdf\';  // the full name and extention of the file as in the $pdf->Output variable above
        $filepath = FPDF_PATH .$filename;
        $components[\'attachments\'] = $filepath; // ATTACH THE NEW PDF THAT WAS SAVED ABOVE  

        // Insert file into CFDB -- Get file contents.
        $tmpfile = fopen($filepath, "r");
        $contents = fread($tmpfile, filesize($filepath));

        // Insert the rows into CFDB.
        $wpdb->insert(wp_cf7dbplugin_submits, array(
            \'submit_time\'   => $file_id,
            \'form_name\'     => $formtitle,
            \'field_name\'    => \'\', // Optional description
            \'field_value\'   => $filename,
            \'field_order\'   => 0,
            \'file\'          => $contents, //the binary contents of the file
        ), array(\'%f\', \'%s\', \'%s\', \'%s\',  \'%d\', \'%s\'));

        $wpdb->insert(wp_cf7dbplugin_submits, array(
            \'submit_time\'   => $file_id,
            \'form_name\'     => $formtitle,
            \'field_name\'    => \'Submitted Login\', 
            \'field_value\'   => $username,
            \'field_order\'   => 9999,
            \'file\'          => NULL, 
        ), array(\'%f\', \'%s\', \'%s\', \'%s\',  \'%d\', \'%s\'));

        $wpdb->insert(wp_cf7dbplugin_submits, array(
            \'submit_time\'   => $file_id,
            \'form_name\'     => $formtitle,
            \'field_name\'    => \'Submitted From\', 
            \'field_value\'   => $ip,
            \'field_order\'   => 10000,
            \'file\'          => NULL,
        ), array(\'%f\', \'%s\', \'%s\', \'%s\',  \'%d\', \'%s\'));     

        }
        return $components;
    } else {
        return $components;
    }
}
add_filter( \'wpcf7_mail_components\', \'mycustom_wpcf7_mail_components\',10,3 );