Uncaught Exception: Some data has already been output to browser, can't send PDF file
in /var/www/html/wp-content/plugins/pdf-print/mpdf/mpdf.php on line 9405

Call stack:

1. mPDF::Output()
   wp-content/plugins/pdf-print/pdf-print.php:1429
2. pdfprnt_print()
   wp-includes/class-wp-hook.php:341
3. WP_Hook::apply_filters()
   wp-includes/class-wp-hook.php:365
4. WP_Hook::do_action()
   wp-includes/plugin.php:570
5. do_action_ref_array()
   wp-includes/class-wp.php:838
6. WP::main()
   wp-includes/functions.php:1343
7. wp()
   wp-blog-header.php:16
8. require('/var/www/html/wp-blog-header.php')
   index.php:17