Installation:
Create a directory in your PAYDAY 3 Steam folder under \PAYDAY3\Content\Paks\ and call it ~mods. Put the downloaded .pak file in this new folder.
Go into your Payday 3 launch options and add -fileopenlog in the field provided.
UPDATE: 07-21-24: Having performance issues? Try using PD3 UE4SS instead of -fileopenlog