In this post i will show u how to enable extension file name, and change the extension files as well.
first, open my documents and go to tools, folder options.
then go to tab view and untick "Hide extension for known file types" and apply.
it is useful when u want to email someone with extension like .exe, .dll because email will detect it as a virus. with this changes, it can bypass email security.
in my case i need file JInitiator from my friend and email it to me. the file is jvm.dll and easily change it to jvm.txt after i download it, i change back to jvm.dll. not a big problem.
bacteria comment: only download and open with file u already know whos your sender is. :D