This could be passports, for example. Every applicant is interviewed when they come in to take the test and at that point we look at their passports to verify their absences from Canada against their declared absences to see if they've been physically present. If there's some evidence that there may have been some tampering with those passports, this would give the authority to a citizenship officer to seize that document.
On April 12th, 2016. See this statement in context.