According to Android Police, Android's built-in download manager doesn't handle downloads made through Chrome. The latest Dev version (Chrome 50) finally allows you to pause and cancel downloads for the first time.
So, if you're trying to download a PDF or MP3 file through Chrome and need to stop it for whatever reason, now you can.
To get the feature right now, you'll need to be using the somewhat problematic Chrome Dev and your phone will need to be running Marshmallow or later.
If you've already downloaded Android N OS to try it out, you'll find that it works there too, but by default different file types are downloaded by different mechanisms, so you shouldn't be confused if different download apps open.
If you don't want to install the Dev version of Chrome on your phone, then you should wait until the next stable version is released.
Of course, there are other browsers for Android, such as Opera which has already given you the ability to pause since 2014.
