code: void decrypt(PdfReader reader) {
          PdfEncryption decrypt = reader.getDecrypt();
          if (decrypt != null) {
              originalValue = value;
              decrypt.setHashKey(objNum, objGen);
              bytes = PdfEncodings.convertToBytes(value, null);
              bytes = decrypt.decryptByteArray(bytes);
              value = PdfEncodings.convertToString(bytes, null);
          }
      }
docs: Decrypt an encrypted <CODE>PdfString</CODE>