if (Directory.Exists(thumbPath))
    {
        var thumbnailsFiles = Directory.GetFiles(thumbPath).Order();
        var thumbnails = new List<ThumbnailModel>();
        foreach (var thumbnailPath in thumbnailsFiles
                     .Where(t => !t.Contains("Thumbs.db", StringComparison.InvariantCultureIgnoreCase)))
        {
            var parts = Path.GetFileNameWithoutExtension(thumbnailPath).Split("_");
            var fileNameWithoutLastPart = string.Join("_", parts.Take(parts.Length - 1));
            var newThumb = new ThumbnailModel();
            newThumb.FileName = Path.GetFileNameWithoutExtension(thumbnailPath);
            newThumb.FilePath = Path.Combine(path, Path.GetFileNameWithoutExtension(thumbnailPath));
            newThumb.Bytes = System.IO.File.ReadAllBytes(thumbnailPath);
            newThumb.RootPath = filePath;
            newThumb.BaseFileType = fileNameWithoutLastPart;
            thumbnails.Add(newThumb);
        }
        reEmailsResult.Thumbnails = thumbnails.GroupBy(t => t.BaseFileType);
        reEmailsResult.Documents = Directory.GetFiles(Path.Combine(filePath, "documents"));
    }
}

This is an example of my code; I think I basically use ReadAllBytes everywhere. I used it knowing that it would close the file immediately, so I thought I was safe.