27D notebook (3)
I believe the answer is:
Here is my best explanation:
'notebook' is the definition.
'27d' is the subsidiary indication.
I cannot really see how this works, but
'27d' could be 'd' and 'd' is present in the answer.
The remaining letters 'pa' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
(Other definitions for pad that I've seen before include "Jotter; compress", "Absorbent material", "Floating leaf of a lily", "Block of paper sheets", "Helicopter stand", "Guard against impact", "Protective guard; home", "It's found on an animals's foot and a cricketer's leg", "Person's home; jotter" and "Sole".)