Device name: Samsung Galaxy J7 Prime (SM-G610F)

From "Settings > About Chrome"
Application version: 58.0.3029.83
Operating system: Android 6.0.1

URLs (if applicable): Any kind of url which opens a (.pdf)

Steps to reproduce:
(1) Click on the url which leads you to a (.pdf) file.
(2) It automatically pops and download begins.
(3) File name changes to an ordered number.

Expected result: 
Should invoke an action asking whether to download or not. Also, inbuilt plugin can be used to open pdf files online 

Actual result:
Auto download of files