Thanks for the info. The problem is that it's a macro that has to check that certain data has been filled, so if it doesn't launch itself (when saving or closing the file for example) it is no longer of any interest.
As for the site you recommended to me, I tested it but nothing happens.
If anyone had another idea.
If you had a piece of code that just launches an msgbox for example when saving a file (a plan in this case), it would be great!
I also lean towards the solution proposed by glaffont.
I would add that to make sure that everyone uses it, the best thing to do is to create a clean installation of SoidWorks, then remove the "save" button and replace it with the same icon with your macro assigned (I don't know if it's possible to do it for the "File > save" menu too, you have to test).
Then you save your settings to deploy them to all users.
Thank you to all of you. That's okay, I solved my question with this link. By downloading macro 1 which launches a userform in the background that never appears.