When you decide to make the move to Windows Server 2012 for you Active Directory Federation Services server, there are a few things to keep in mind. First is the migration process for ADFS on Windows Server 2008 R2 to Windows Server 2012. The second one is if you as an organization are using ADFS with Office 365. If you are using Office 365, then the relying trust can not be added back manually like the first document says. Office 365 automatically created this when running the federation command in PowerShell when you originally federated the domain to Office 365. You would need to repair the relying trust with PowerShell. Follow these instructions from Microsoft.