In the form properties, design tab you have an option to disable printing/forwarding/copying to clipboard of the document created using the form. By enabling this feature all documents created using this form will be locked for printing/forwarding/copying to clipboard. Here's the method to enable this feature to prevent a single document in a database from being printed, forwarded or copied.
Create a text field $KeepPrivate in the form. The value of this field can be set to "1" to enable and "0" to disable the document being copied or printed.
Note: Once the field $KeepPrivate field is created in the form, the form property disable printing/forwarding/copying will not be used. So the value of $KeepPrivate should be set to "1" or "0" through your design to enable or disable this feature.