[JavaScript Error: "Error: Could not remove C:\Users\[…]\AppData\Roaming\Microsoft\Word\STARTUP\Zotero.dotm" {file: "resource://zotero-winword-integration/installer.jsm" line: 181}]

This could be due to security software on your computer preventing Zotero from updating the plugin. You can try fixing that so that future updates work automatically. Otherwise, delete the above Zotero.dotm file manually, restart Word to make sure that the Zotero toolbar is completely gone, and then follow the manual installation instructions to reinstall the latest version of the plugin.

Check to see if Word (or Zotero) is running as administrator, and if it is fix it to run as the normal user:

https://superuser.com/questions/1213101/check-if-an-app-is-running-as-admin

More troubleshooting:

https://www.zotero.org/support/word_processor_plugin_troubleshooting#communication_error_or_non-responsive_plugin_buttons

French is fine, but you need to say more than that. You have to say what you actually did and what happened at each step.

No, that's not sufficient. We need you to say, in your own words, what you tried and what happened at each step.

j'ai vérifié que j'étais bien en administrateur

What exactly do you mean here? The point is that you need to check that neither Word nor Zotero is running as administrator. If you've done so, you need to say that clearly — and please say exactly how you determined that.

No, neither should be running as administrator.