This policy will prevent opening of Word documents with HTML file types such as *.htm, *.html, *.mht, *.mhtml.
| Registry Hive | HKEY_CURRENT_USER |
| Registry Path | Software\Policies\Microsoft\Office\12.0\Word\Security\FileOpenBlock |
| Value Name | HtmlFiles |
| Value Type | REG_DWORD |
| Enabled Value | 1 |
| Disabled Value | 0 |