Here’s a simple windows batch script that has the ability of copying a file from the device’s system folder to your desktop:
adb shell su -c cp data/data/[system app name]/databases/app.db /sdcard/Download/; exit;
adb pull /sdcard/Download/app.db "C:\Users\[your username]\Desktop"
adb shell su -c rm /sdcard/Download/app.db;
Just save the above text to a text file and rename the extension to .bat and execute.
Do not end the path to your PC with a back slash, it will not work.
Replace [system app name] with the remaining path to your system app and, replace [your username] with the remaining path to your desktop or, replace with some other path on your PC.
Tested on a rooted phone only.