password protected pdf file.

Hi Team,

In my application i am checking whether a pdf file is password protected or not.

After so much R&D i am using the following function to check this.
I know this is not a straight forward method. But this was working for all the type of pdf passwords.

The application is crashing at this point  :  info = new PdfFileInfo(FileName);

 public static bool IsPDFPasswordProtected(string FileName)
        {

           // bool isPassProtected = false;

           // PdfFileInfo fileInfo = new PdfFileInfo(FileName);
           // // determine that source PDF file is Encrypted with password
           // //if (fileInfo.IsEncrypted)
           // //{
           // //    isPassProtected = true;
           // //}
           // //return isPassProtected;
           //// return isPassProtected = fileInfo.IsEncrypted;



           //  if (fileInfo.HasOpenPassword || fileInfo.HasEditPassword)
           //  {
           //      isPassProtected = true;
           //  }

           //  return isPassProtected;


            bool flag = false;
            PdfFileInfo info = null;
            try
            {
                info = new PdfFileInfo(FileName);
                //if (info.HasOpenPassword)
                //{
                //    flag = true;
                //}
            }
            catch (IOException exception)
            {
                if (exception.Message.ToUpper().StartsWith("BAD PASSWORD"))
                {
                    flag = true;
                }
            }
            catch (Exception exception2)
            {
                throw exception2;
            }
            finally
            {
                if (info != null)
                {
                    try
                    {
                        info.ClearInfo();
                        info = null;
                    }
                    catch (Exception)
                    {
                        flag = true;
                    }
                  
                }
            }
            return flag;
           
        }

But suddenly  when i am processing the attached pdf file through this code my application is crashing.

Can you please help me on this ?
Regards
Anish