Question: how to add ajaxcontroltoolkit.dll in visual studio?
Answer: Download and Copy the AJAX Control Toolkit DLL. The very first task is to download the AJAX Control Toolkit DLL using the following download link. ...  Add a New Tab in ToolBox. Now you need to open Visual Studio, right click in the ToolBox and click Add Tab. Set a suitable name for the Tab. ...  Choose Items for the ToolBox.