No, the i9-9900K is not compatible with the Z170P-D3.
No, the i9-9900K is not compatible with the Z170P-D3.
It won't function properly. The top CPU for this motherboard is an i7 7700K (after BIOS update) or a 6700K. Your existing CPU and the 9900K both use LGA 1151 sockets, but with that socket you have v1 and v2 options.
These processors don't match with the board types, making it safe but causing issues