Telerik License Watermark Appears When UI for WinForms Form is Used in Add-In Project

Environment

Product Version	Product	Author
2025.3.812	Telerik UI for WinForms	Dinko Krastev

Description

The invalid/missing Telerik license key dialog is shown in addin (like Excel VSTO Add-in) projects even when a valid license is installed.

Solution

This happens because there is no proper main window and application context, which means that the licensing mechanism cannot be evaluated as expected. To resolve this, use the TelerikLicensing.Register static method.

Here is a possible solution to resolve the licensing mechanism and remove the Watermark if the license key is valid:

• Ensure that each project library in your Add-in/Plugin Project is referencing the Telerik.Licensing NuGet. The Licensing NuGet is located on the NuGet.org server.

• Ensure that the watermark does not appear in your Add-In/Plugin when run as a standalone application in Visual Studio.

• Call the TelerikLicensing.Register() method as early as possible, before initializing any Telerik controls. Keep in mind that RadForm is also a control from our suite. You will need to consider placing it as early as possible in your plug-in’s loading process.

public class TelerikHelper
{
    public static void Register() => Telerik.Licensing.TelerikLicensing.Register();
}