The hiberfil.sys is created and used when hibernating in Windows. Sometimes can be needed to help shrink the space on a drive.
Launch a command prompt with administrator privileges.
You can hit Windows Key + R, type in cmd, and hit Ctrl + Shift + Enter together. It’ll ask you to verify that you want to launch it. Hit Yes.
Alternatively you can search for the Command Prompt, Right click on it and Run as Administrator
Turn Hibernate off
powercfg -h off
A reboot should remove the file. If not you should be able to delete it. It is on the root of the drive, but you’ll need to enable hidden files and disable the “Hide protected operating system files” to see it.
You can turn it back on by changing off to on
powercfg -h on