This blog defines how to list all files matching search pattern in directory and subdirectories.

/// <summary>

/// Lists all matching search pattern filenames and filesize in directory
/// </summary>
/// <param name="rootDirPath">root directory path like C:\test\</param>
/// <param name="searchPattern">file search pattern like *.js for searching all javascript files</param>

private static void ListAllFilesInDirectoryAndSubdirectories(string rootDirPath, string searchPattern)

{
var dir = new DirectoryInfo(rootDirPath);
if (!dir.Exists)
{
Console.WriteLine("Directory doesn't exists: " + dir.ToString());
return;
}

DirectoryInfo sourceDir = new DirectoryInfo(rootDirPath);

FileInfo[] files = sourceDir.GetFiles(searchPattern); //Get only files which you need to work with.
foreach (var myFile in files)
{
 try
{
Console.WriteLine("Filename:" + myFile.FullName);
Console.WriteLine("Filesize:" + myFile.Length);
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
 }
DirectoryInfo[] subDirectories = sourceDir.GetDirectories(); //Get subdirectories
foreach (var subDirectory in subDirectories)
{
ListAllFilesInDirectoryAndSubdirectories(subDirectory.FullName, searchPattern);
}
}