/// <summary>
		/// Returns true if the filetype uploaded has an accepted extension.
		/// </summary>
		/// <param name="filename"></param>
		/// <returns></returns>
		private bool ValidFileType(string filename)
		{
			if (filename.Length == 0) return true;
			string uploadedFileExtension = Path.GetExtension(filename).Substring(1);



			foreach (string extension in ValidFileExtensions)
			{
				if (uploadedFileExtension == extension) return true;
			}
			return false;
		}

Validate upload filetype

C#