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"

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

It is possible to manually edit robots.txt now. You can add

Disallow: /*.pdf

to your robots.txt