Microsoft has increased its driver signing security policy in its latest 1903 update. The update is only needed by buyers who purchased Realtrim Professional before 06.10.2019 and want to do a new installation under Windows 10 1903. RealTrim Professional will continue to work if the upgrade to Windows 1903 was not performed until after the previous installation of RealTrim Professional. Before you install the new version, you must completely uninstall the old one. A restart after the uninstallation is necessary.

You will finde the update you will find the update in the support menu.