TraverseDirectory

using System;
using System.Collections.Generic;
using System.IO;

public class Program
{
    private static List<string> files = new List<string>();

    public static void Main()
    {
        string rootPath = @"C:\Program Files (x86)";
        string fileExtension = "*.dll";

        TraverseDirectory(rootPath, fileExtension);

        foreach (string file in files)
        {
            Console.WriteLine(file);
        }
    }

    private static void TraverseDirectory(string currentPath, string fileExtension)
    {
        string[] currentDirFiles = Directory.GetFiles(currentPath, fileExtension);
        files.AddRange(currentDirFiles);

        string[] curretDirDirectories = Directory.GetDirectories(currentPath);
        foreach (var dir in curretDirDirectories)
        {
            TraverseDirectory(dir, fileExtension);
        }
    }
}