Check file size in C#

Hello,
at the first i am very sorry if it is the wrong section to post a question.
I have just started to learn C# and i have done my first program, i wanted to avoid illegal users so i decided to make a size checker for the folder of my program.
can some give me a example to do that? or is it possible.
Thanks and sorry for any kind of mistaking or stupidity :handsdown:.

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searched in google and had that link before but it didnt open