Built into Acrobat is a dynamic approval stamp. It is dynamic by including the name of the user, the time and date of the stamp. The first time it is selected, a dialog will appear requiring the user to add their name and at minimum, their email address.

The commenting functionality is available in the free Adobe Reader, when the PDF has been sent from a user with a full version of Acrobat through the Comment Review process or Reader enabled, by a user of a full version of Acrobat.
For users of Reader the Comment & Markup toolbar will automatically appear on a PDF that has been enabled. For users of a full version of Acrobat select Comment> Show Comment & Markup Tools.

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