Pen Window Manager is a simple app that will allow you to use the Pen window feature found on the Galaxy Note 3 for any app! To use this app you will need to be rooted, you should have a backup of your current system incase something goes wrong or you decide you don't like the mod and want to revert, Download the apk from the source link and install it like you would a normal apk, Open the app and tick the apps that you want to use with Window Manager, lastly click the save button to save your settings. You can grab this app for free from the source link.
Via XDA
Via XDA