Suddenly without taking my permission my surface pro shows a screen saying "Restarting" and then the windows 10 restarts and close all the running apps and documents without saving ! is that a system crash or what's going on ?? how can the windows restart based on it self ..
Not many details provided by you, but a restart like this is rare, but usually means that Windows is saving you from a serious incompatibility of software or firmware, drivers or OS, and a restart MUST happen. Without the restart, your files might be more at risk.
This may be a newly configured SP4. Also, you may have been warned earlier that a restart must happen by software you installed, or updates which were applied.