Let me see if I understood your question correctly.
When you boot the OS from a HORM [hibernate] state at run time you want to know whether the system started cold boot or was resumed
from the hiberfil.sys file. Right?
You can't open the hiberfil.sys file from the same OS. The system keeps the file locked if hibernation feature is enabled.
You can try to use the existance of the resmany.dat at the root of the system volume as the indicator. The resmany.dat file is used
to notify ntldr to boot from the hibernation file. The ntldr changes the signature of the hibernation file when it is first booted
(this is probably what you were trying to check, right?).