Prevent google from indexing pdf files

Is there anyway to prevent search engines like google from indexing pdf files? I know that we can do something like

<Files ~ "\.pdf$">
  Header set X-Robots-Tag "noindex, nofollow"
</Files>

in htaccess for normal websites. But how this is possible for discourse?

Ahora es posible editar manualmente robots.txt. Puedes agregar

Disallow: /*.pdf

a tu robots.txt