Microsoft blocks the installation of old, insecure frameworks (like 4.0) when a newer, compatible version (4.8) is already built-in.
your system.
Only install .NET 4.0.3 if you are running a that cannot be upgraded. .net 4.0.3 download
Need help migrating away from .NET 4.0.3? Consider using the .NET Portability Analyzer to plan your upgrade path. Microsoft blocks the installation of old
Microsoft’s historical download page for the can sometimes be found via the Microsoft Download Center by searching for "Microsoft .NET Framework 4.0.3" – though links often redirect to newer versions. Use the Microsoft Update Catalog for certainty. .net 4.0.3 download