Pulling an apk of paid app from the device
You wont be able to pull a "protected app" without root, sorry.

This has nothing to do with the app being payed, except that usually only payed apps are "protected" (theoretically, free apps could be "protected" as well); think of it rather as a kind of "DRM".

Once your device is rooted, you can use "root powers" to pull those .apk files. This can be done either using a specialized app (such as AppMonster), or via adb pull if the ADB daemon runs in root-mode (it usually doesn't, but that can be achieved using adbd Insecure). adb root usually doesn't work on "production devices", so you have to use this different approach.