Adobe Acrobat 7 Professional - Manual (Page 707)

Creating document properties
You can add custom document properties to store specific types of metadata, such as the
version number or company name, in a PDF document. Properties you create appear in the
Document Properties dialog box. Properties you create must have unique names that do
not appear on the other tabs in the Document Properties dialog box.
To create or change document properties:
1. Choose File > Document Properties, and then select Custom.
2. To add a property, type the name and value, and then click Add.
3. To change the properties, do any of the following, and then click OK:
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To edit a property, select it, change the Name or Value, and then click Change.
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To delete a property, select it and click Delete.