When you include attachments in your DDP, for default relationships, the DDP will find attachments related to the record the DDP runs on, as well as it's parent record.
E.g. when running a DDP on Opportunity, attachments form the Opportunity AND it's parent Account will be available.
I need to be able to exclude the Account level attachments from the selection list so that the Users do not see them when running an Opportunity level DDP