Hello,

A solution to my problem was indeed given in this web page
https://www.emacswiki.org/emacs/AutoInsertMode:

#+BEGIN_QUOTE
(auto-insert-mode)  ;;; Adds hook to find-files-hook
    (setq auto-insert-directory "~/.mytemplates/") ;;; Or use custom, *NOTE* Trailing slash important
    (setq auto-insert-query nil) ;;; If you don't want to be prompted before insertion
    (define-auto-insert "\.py" "my-python-template.py")
    (define-auto-insert "\.php" "my-php-template.php")

It should not be too difficult, even for me, to adapt this code that I
just tested.

Best wishes,
–
Jo.