What exactly are you trying to achieve? Create your own AutoText entry for
re-use? If so, look up Autotext in the Help. If you want a button for it to
appear on the Header & Footer toolbar, make sure the toolbar is visible,
then go to Tools, Customize. Click the Commands tab. Scroll down the left
list until you come to AutoText, then click & drag your autotext entry from
the right list and drop it onto the toolbar.

Select the date & press Ctrl-Shift-F9

Primepixie was telling us:
Primepixie nous racontait que :

Insert the autotext as you normally do. Then, place the cursor in the date
field and do SHIFT-CTRL-F9. This will transform the date field in ordinary
text that will no longer update.

To get today's date automatically, you have to use a field, so even if you
created your own without the Auto-update feature, the date would always be
wrong when you inserted it.

Just so you now, to create an AutoText is easy.

Select he text you want to use as an autotext (Make sure not to select the ¶
(Click on Show All to see those - the ¶ next to the zoom on the toolbar)
that follows the text unless you want to preserve the current formatting
with he autotext - of course, if you have more than one paragraph, then you
have to select the ¶'s).
Then, Insert > AutoText > AutoText...
Give the autotext a name at the top, select the template where you want to
save the autotext at the bottom (if you do not know about template, ignore
this step), then click Add. You are done.