I had planned to provide similar functionality, so I collected some
links on the subject. I never did, so I can't attest to one method or
another.

http://www.google.com/groups?hl=en&l...ff0506a&rnum=1
http://www.google.com/groups?hl=en&l...c341ef8&rnum=2
http://www.google.com/groups?hl=en&l...f48af05&rnum=1
http://www.google.com/groups?hl=en&l...%40tkmsftngp04
http://www.google.com/groups?hl=en&l...ff4fa2e&rnum=5
http://www.google.com/groups?hl=en&l...bbfde7&rnum=28
http://www.google.com/groups?hl=en&l...5a9880&rnum=35

HTH
Paul
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Be advised to back up your WorkBook before attempting to make changes.
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I want to a establish a trial period of 30 days from the day the user
first opened the workbook. The user will not need a password when
opening the workbook within those 30 days. After that he will need a
password to use the application.
I have received some excellent advice on the password issue.
Does anyone have any ideas how to do the trial period?
Thanks,
Nathan