The .NET Framework 4.5 Developer Pack (also known as the Targeting Pack) is an essential set of components for software developers who need to build, compile, and debug applications that target the 4.5 version of the framework. While the runtime allows a computer to run 4.5 apps, the developer pack is what allows Visual Studio to create them. Direct Download Links
– Used specifically for legacy projects that must target the 4.5.1 revision.
These are "empty" versions of the libraries that contain only the metadata. They tell your compiler and Visual Studio which classes and methods are available in .NET 4.5.
The following official links lead to the Microsoft Download Center for the different iterations of the 4.5 series:
Unlike a standard runtime installer, the developer pack is a bundled installer that provides several key components for your development environment:
Includes the actual .NET Framework 4.5 binaries required to run and test the application on your machine.
Provides the hover-over documentation and code completion hints you see while typing in Visual Studio.