Where does Android store the "default application for file type (open with)" settings? Where does Android store the default application settings that connects each type of content with a designated application?
I mean which application open each kind of file or content type so if I got two PDF readers and I downloaded a PDF file android will use one of them without letting the user an option to choose.

I know I can clear the default settings of an application but it's not what I'm looking for.

I want to find the table/database/file that android uses for this.
Is it in a sqlite database file? Where is it stored ?
On Jelly Bean, the preferred activities are stored in the XML file /data/system/users/0/package-restrictions.xml for the primary user. Other users have their user ID in place of 0 in that path. If encrypted file system is enabled, it starts with /data/secure/system instead of /data/system.

Other than through the PackageManager service, this file can only be accessed by root. You can see the code that reads and writes the file (and thus infer the format) in the class com.android.server.pm.Settings.