Reading file names is pretty easy:
string[] files = Directory.GetFiles(@"D:\Temp");
If you want the filename without the path then add:
string[] justFiles = files.Select(f => Path.GetFileName(f)).ToArray();
Or
string[] justFiles = files.Select(f => Path.GetFileNameWithoutExtension(f)).ToArray();
Saving to Excel is more complex, but this may help simplify it:
Write Data to Excel using C#[
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