On , I learnt ...
How to read from one buffer to another in Vim
Refer to the buffer’s number using a hash. For example, run:
:read #3
to insert the contents of the file linked to buffer 3. Note that a buffer’s content isn’t necessarily the same as the linked file.
From: https://stackoverflow.com/questions/37859530/vim-how-to-read-from-one-buffer-into-another