Encryption Password Expires in 30 Days

[Rob]

Hello,

I am using Excel 2007. I have an encrypted document that is password
protected. I am fearful of this document winding up in one of my competitors
hands. Is there anyway to have the password expire after so many days (for
example 30 days) and the workbook simply won't open? I am thinking you are
asked for the password but no matter what you enter the workbook simply won't
open.

Thanks for your help!!