Why is this necessary?
The apps on the Mac App Store must be sandboxed, it means they can't communicate with other apps so there is no way to implement the Direct Paste feature in the App Store version of Paste. We have introduced an optional Helper application which makes Direct Paste work.
The first time you turn on Direct Paste, it will prompt you to download the Helper application. Paste Helper installs itself to ~/Library/Application Support/Paste Helper directory and runs in the background.