The easiest way to get the latest version (v20.1.0) is via the AjaxControlToolkit NuGet Gallery .
The ( AjaxControlToolkit.dll ) is the core assembly for the ASP.NET AJAX Control Toolkit , a free, open-source library that provides over 40 interactive controls for building responsive web applications. 🚀 Getting Started Ajax Control Toolkit Dll File
If you download the ZIP file manually, you must right-click the file, select Properties , and click Unblock before extracting. The easiest way to get the latest version (v20