If you see dozens of DLLs, the pack is installed. If you get a "File Not Found" error, the pack is missing.
If you are migrating legacy projects to the modern SDK format ( .csproj ), specify multiple targets: microsoft .net framework 4 multi targeting pack
You need the Microsoft .NET Framework 4 SDK (part of the Windows SDK for Windows 7 and .NET Framework 4). If you see dozens of DLLs, the pack is installed