How to use reflection in C# to extract class and method information from executable file(.exe)

I have .exe file generated via visual studio. Now, in a reversed way, I need to get classes info (namespace and class name) and method info (access modifier, return type, and input parameters) from .exe file.

Actually I could get those info from dll files, but no idea from executable files.

Could anyone give me a simple code demo? Thanks in advance!!