PDM library - using with nRF52840

I'm using SDK 16.0.0.

I wish to use two MEMS microphones to record audio over the I2S interface, and then send it over Bluetooth.

What is the best library to use for this? I've found  "nrf_drv_pdm.h" in integration/nrfx/legacy, but the .c file is not present.

Thanks for your assistance.