How to determine the assembly compiled in which version of .net
To determine the assembly is compiled in which version of .net, you can use use Assembly.ImageRuntimeVersion.
You may learn the Assembly.ImageRuntimeVersion Property from here: https://msdn2.microsoft.com/en-us/library/system.reflection.assembly.imageruntimeversion(vs.80).aspx
There is a blog discusses on that: https://blogs.msdn.com/suzcook/archive/2003/06/20/57191.aspx