I can't Kill or Close the external exe that i already opened from the unity exe ?

Hello All i am trying to create a simple unity scene that will be able to open another exe files on my pc , ok ? i did that already but when i try to make back again to the main unity app by close the current process that i have already opened , it doesn't ! ? so why that is my code BTW when i try to print (p.id) or print (p.name) it is working , that is mean that i success to access the current process so what is wrong here as you see i use all parameters that could help me Close closemainwindow Kill so what is wrong ? Thanks in Advance i am using unity2017.2