If an Approval workflow assigns a task to approve a document to a user, that user receives an email which prompts them to:
Does being assigned the approval task automatically elevate the user's permission levels in order to allow them to carry these actions out, or do they already need to have
The workflow itself does not elevate the rights of the users permission levels (the workflow itself runs in the context of SHAREPOINT\System context)
The user in question would need edit permissions to the document library and the task list.