Adobe Acrobat 7 Professional - Manual (Page 345)

Removing user security policies applied to a document
Use the Remove Security Settings For This Document command from the Secure menu in
the Tasks toolbar to remove a user security policy from an open PDF document. If you
made a PDF document available to a group of users and if you want to revoke permission
to open it, you can change the policy. For details on editing security policies, choose
Secure > Use APS Web Console from the Tasks toolbar, and then click Help.
To remove security from a PDF document:
From the toolbar, choose Secure > Remove Security Settings For This Document, and
then click OK.