How do I copy a clip from Playlist in File #1 and paste it into File #2?
Export the playlist item as a clip - i.e. a piece of footage you can use anywhere, then you can import it into any project you wish.
I’m not aware of a facility to copy a playlist item between projects (believe me - I’ve tried) but I’ll keep an eye on this thread in case there’s a useful trick I don’t know about 
Export it as like a mp4? That would degrade the quality, though.
Set the quality settings to their max of course and use a lossless format if you want max fidelity. You will eventually be exporting it anyway so some slight loss due to compression is inevitable.
The other option I can see would be to create a timeline with ONLY your clip on it, save the MLT, then in your other project, choose the “import MLT as clip” option. It’s a longer route, but would get you to the same place without any degradation along the way.
Thanks. I discovered that second solution on my own, except I dragged the mlt to the Playlist. Same result.