The PDK is created by the foundry defining a certain technology variation for their processes.
The customers may enhance the PDK, tailoring it to their specific design styles and markets.
The data in the PDK is specific to the foundry's process variation and is chosen early in the design process, influenced by the market requirements for the chip.
An accurate PDK will increase the chances of first-pass successful silicon.
Different tools in the design flow have different input formats for the PDK data.