While .NET 4.5 was a major milestone, it is important to note that Microsoft has released newer versions like 4.6, 4.7, and 4.8. For the best security and compatibility with the latest apps, you should generally aim for the highest version your OS supports—which for Windows 7 is .
.NET 4.5 is not backward compatible with .NET 3.5 or 2.0. If you need older applications, you must install those separately (via Windows Features). Conversely, .NET 4.5 is forward-compatible with .NET 4.5.1, 4.5.2, 4.6, and 4.7 (most apps built on those will run on 4.5). microsoft net framework 4.5 offline installer for windows 7