How to make sub folder of public directory accessable in Symfony?

I've got a problem in Symfony PHP Framework.

I have some files that I want to serve so it can be downloaded directly. I put my assets in /public/pdf/. Let says i have book.pdf file, Then if I want to download book.pdf I just type http://host/pdf/book.pdf. But it show :

No route found for "GET /pdf/book.pdf"

I double check if there any misspell, but there are not. The route always use index.php to route.

Then I search on stackoverflow, I found this question. But I must create controller first, then serve it on BinaryResponse. That isn't something that I want.

How can I download directly from the subfolder of public/ directory on Symfony?