How to allow pdf files in .htaccess?

I have this following codes in my htaccess file, but it doesn't allow pdf file to open, it will redirect to 404 page. how can I allow pdf files to open based on my following htaccess file. RewriteEngine on RewriteCond $1 !^(index\.php|images|public|assets|uploads|themes|updates|asset|mob|robots\.txt\.pdf) RewriteRule ^(.*)$ index.php?/$1 [QSA,L] Header set Cache-Control "max-age=604800, public" I highly appreciate your help. Thank