A pad upvc door handle is generally used on front doors to ensure the door locks each time after entering. Some pad upvc door handles can be inline but still work of two spindles. Other types of pad handles can be dual spindle with offset levers.
The whole idea behind a pad upvc door handle is to provide some functionality for keeping the doors more secure after entry. It could also be argued that the design of the pad lever offers an easier lever to grasp. The more common types of upvc door handles are single spindle handles and in this case the door remains unlocked after entry and until the key is then used.
Offset or Dual Spindle Pad uPVC Door Handles
A pad upvc door handle with levers that are offset to each other have a pad in a lower position than the internal lever (with one older handle exception). When you close the door the door can only be opened from the outside with a key. When locking the door on exit the pad can be lifted to engage the multi-point locks and then key locked. Greater care needs to be taken when replacing these types of handles. Follow the advice here on how to measure upvc offset door handles.
Inline Split Spindle Door Handles
This type of spindle arrangement means you have two spindles meeting in the middle of the lock. The lockcase is designed in such a way that the central drive where the spindle fits into can operate independently each side. In other words one spindle can turn the lock while the other spindle doesn't move. A spring pushes the spindle into the middle to engage.
Take a look at this product video showing a pad upvc door handle design and how offset spindles and single spindles operate.