Playing Negative Doubles, Opener's partner cannot double for penalty directly.

1 2 X
would tend to show at least 4 cards in either unbid suit and 9+HCP.
Axxx Kxxx Qxx xx for example

What if instead you wish to penalize, sitting after the 2C bidder?
KQx xx xx AT9876 for example
You have to pass and hope partner 'reopens'.
1 2 P

If Overcaller's partner also passes, Opener should at least consider a 'reopening double'.
1 2 P P
X!

What is a reopening double?
It is NOT a penalty double.
It should be a hand with no more than 2 of the Overcaller's suit.
With 3 or more cards in the opps suit, Opener should prefer passing or rebidding NT (18+ balanced).
Re-opening also requires at least 3 cards in each unbid suit:

Axx Kxx KQxxx Jx is one of the WORST cases.
Axxx AQxx AKQx x is one of the BEST cases.
Both are hands that should be "reopened" with a DOUBLE.