You cannot see files in DDMS, but you can get a list of the locations of all files with the command:
adb shell pm list packages -f
(you can also add an optional additional parameter to restrict the listed files to those that correspond to your additional parameter).
Once you have the file location, you can execute a command, for example
adb pull /system/app/GoogleEarth.apk
to actually download the file from the device and to the PC.
None of this requires a rooted device.
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