New
#1
This will be part of the firmware - I doubt there is an actual file - at this stage you have not started windows.
Why do you ask?
The Windows Boot Manager BOOTMGR file.
Used to be in the days of DOS and early Windows, maybe into WinME or Win2000 it would have been using the PrntScrn key with a Parallel Port printer. The advent of later versions of Windows and USB printers changed things and basically the PrntScrn key sends the image to the Clipboard after the OS has loaded but not during the startup phase.