how do i copy a thread in text messages and copy into a note pad app?

Tap and hold a bubble, and select More. Put a checkmark beside each bubble you want to copy, then hit the arrow at bottom right. This will open a new message with the copied text in the text entry box. You can copy all of this and paste into Notes, but you lose who it came from unless you edit that in yourself.

You can also take screenshots of each window of text bubbles.