protected readonly static List<string> VALID_FILE_TYPES = new List<string> { "pdf", "PDF" };

    protected bool ValidateFileType(string fileName)
    {
        string fileType = String.Empty;
        int lastDotIndex = fileName.LastIndexOf(".");
        if (lastDotIndex >= 0)
        {
            fileType = fileName.Substring(lastDotIndex + 1).ToLower();

        }

        if (VALID_FILE_TYPES.Contains(fileType))
        {
            PageClass.PDFFileType = fileType;
            return true;

        }
        else
        {
            return false;
        }
    }