If you open up an executable and realize it's .net
then you try using ilspy or dnspy but it's simply not readable, tons of unicode and other things
give de4dot a try
https://github.com/Robert-McGinley/de4dot-Installer
it's as sample as running the command
de4dot.exe Obfuscated.exe
and it will create a new cleaner file called
Obfuscated-cleaned.exe
then re-open that cleaned file in ilspy or dnspy and hopefully it'll be more readable