PhpStorm interface

New user here, and I could not find an answer in the help, settings or KB. Basically, while I also use projects, many times I need to quickly edit a PHP file somewhere on my PC. When I double click the file, PhpStorm opens it just fine, but always with the "Project tool window" open, occupying one third or more of the screen. I really do not need this pane all the time, and having to close this pane or pressing Alt-1 each time I start the application does seem strange. Even with the pane closed, removed from the sidebar, and after using "Window > Store Current Layout as Default" does not help at all - the pane is always back and open the next time I open a file. If somebody could let me know how to address this, I would be grateful. I suspect there is a setting, but where?