An Azure service that is used to provision Windows and Linux virtual machines.
When you enable PIM, it will not affect any users with existing permanent access roles, this will stay as they are. If you wish to convert these from permanent to PIM roles you will need to go through the process to do so. If you don't want to do this manually, then you can use PowerShell and the PIM cmdlets to help do this for you, but there is no built-in automation to do so.