detect that winform was run by program.cs or other location

I have one file userlogin.cs - that runs by program.cs automatically.

I want to close userlogin on opening mdiform , But when i close it , Then all pages are closed.

I want to check weather given file is opened by program.cs or by other location like log out form.

If it was opened by log out form , then i want to close it." I dont know how to Search it

Thank You

Vishmay