In Emacs, how do I copy a region of text (to paste it in another buffer) without killing it (for example: the file I want to copy from is opened in read-only mode, so killing it isn't an option).
Just mark it (C-space at one end of the range, and move to the other end) and use M-w (kill-ring-save):
kill-ring-save
(kill-ring-save BEG END) Save the region as if killed, but don't kill it.
(kill-ring-save BEG END)
Save the region as if killed, but don't kill it.