I have a surface pro 3 that when I booted up this morning received a digital Signature file couldn't be verified.

windows\system32\winload.efi

How do I recover

Does it happen when you boot into Windows or before booting to the Windows?

Did you upgrade to Windows 10 from Windows 8.1 or is it the issue with new Windows 10 build?

Something like this : http://answers.microsoft.com/en-us/windows/forum/windows_8-system/filewindowssystem32winloadefi-error-code/cf874f7f-d9d0-477d-a808-a4d45afbd523