How do I get Arduino to edit and include a file?

Pretty basic Arduino question - so I am trying to edit a third-party plugin. It’s a cpp file, so in order to open it in Arduino, I have to use the “Add File” command, which copies the file into the sketch I’m using - but then when I edit it and compile, the file that is included is the original, not the one I copied and edited.

How do I get it to include the one I’m editing instead, or is there a better way to do it?

Is the original in the Arduino library folder or still opened in Arduino IDE when compiling - as that may cause the opened file to get compiled as well as your sketch, if I remember correctly. If you just drop the files next to your sketch file, it should be fine.

Arduino will not open the original. It will only create a copy and open that. The copy is the one I edited and have open in the IDE. The original is in a library folder.

I’m not sure what you mean by “drop the files next to your sketch file” - can you clarify please?