Whats the difference between WindowsNoEditor.pak and WindowsNoEditorP.pak?

I would like to edit some files, but there are 2 pak files…

WindowsNoEditor.pak
WindowsNoEditor_P.pak

what is the difference? The game was made with Unreal Engine 4… I was able to unpack the pak files and now I see a lot of folders and files with uassets for the extensions… I wanted to make some custom mods to the graphics and sounds… after I finish, how would I re-pak them back?

WindowsNoEditor.pak is the main pak file of the game. WindowsNoEditor_P.pak is patch file which game is generated.