No index and no follow on pdf with smartcrawl

I can not choose to no index and no follow pdf with smarcrawl. I have tried this in htaccess
<FilesMatch "\.pdf$">
header set x-robots-tag: noindex
</FilesMatch>

and also tried to add the following in robot.txt file
Disallow: /*.pdf
but it did not work, could you please share me a functional line of code to insert in the robot.txt file