why Microsoft.SqlServer.Management.Smo.Restore could not be found

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C#

SQL-Server

after i looked the tutorial in code project Restore Database during Application Deployment[^]

i have already make referenced to Microsoft.SqlServer.Management.Smo.dll and declare namespace

but the following code shows the error type or namespace name 'Restore' could not be found

Restore sqlRestore = new Restore();

            BackupDeviceItem deviceItem = new BackupDeviceItem(filePath, DeviceType.File);
            sqlRestore.Devices.Add(deviceItem);
            sqlRestore.Database = databaseName;

how to solve this error