Hiberfil.sys is the file used by default by Windows to save hibernation file. It is saved in the system root directory, takes up the same system spaces as memory compacity. As a result, we need to move hiberfil.sys to another volume to free up C volume space in Windows 10.
In general, hibernation function is on. When Windows 10 gets into hibernation status, your computer will be shut down and all contents saved on the memory saved to the hard disk. Once the system is wakened up, the formerly open programs and files are restored to the desktop.
As a system file, hiberfil.sys is hidden. To view hiberfil.sys file, you can open File Explorer Options window then click on the View tab and uncheck Hide Protected Operating System Files (Recommended) option.
Here is the guidance to move hiberfill.sys to another disk in Windows 10.
In some PC, hiberfil.sys is unable to move to another volume. Because of Windows system must load the filesystem driver program if it reads the booting files from other places on hard drive. However, hibernation system's filesystem driver program is inside the hiberfil.sys. It can't load outside the system partition. As a result, hiberfil.sys file can't read without loading filesystem driver program. This is why you can't move Windows 10 hiberfil.sys to another volume.