I always deal with many opened files in Notepad++, and I always need to copy there file name or path.

I suggest:
1)the opened window from "Window"->"Windows" can copy the selected files "Full file path to Clipboard", "File Name to Clipboard", "Current dir path to Clipboard", and also set the selected files to read only.

2) The Open Window Dialog (Ctrl+O) contains options for open the files in read only mode.