HTC has long used the Play Store to update some of the system components on its phones, and the latest arrival is HTC PNS, which presumably stands for push notification service. This is the app that handles notifications from all the HTC stuff on your phone.
This isn't a new system component—the push service is already on HTC's phones, but now it's updated via the Play Store independently of the HTC Device Management module. Now HTC can add new features to its push messages without a full system update.
The listing gives several examples of the sort of content you might see thanks to this updated app. Maybe you'll see notifications for new themes, activity on Zoe (assuming you use it), or messages in the HTC community app. I'm sure it could also be used for ads of some manner, but let's hope not.