Get the Whitepaper called Microsoft Excel Spreadsheets Expose User PIN Used For Confidential/Secure Printing.
You can download it from the following link: https://packetstormsecurity.com/files/download/98025/msexcel-userpin.pdf
Source: https://packetstormsecurity.com/files/98025/Microsoft-Excel-Spreadsheets-Expose-User-PIN-For-Secure-Printing.html