Use the export tool to extract pak files into a folder and back: https://github.com/Norbyte/lslib/releases/tag/v1.18.7

The BG3 Mod manager also can extract them, which is sometimes more convenient if you just want to quickly extract a pak to the desktop, to see how stuff was done there. The original files of most things changed in mods are in the Shared.pak in the game's data folder. UI stuff is in Game.pak.

And I hope you use Notepad++ not the Windows notepad (unless you're a disciple of Loviatar, then go you!)