If you assign a document or questionnaire the Restricted - High or Restricted - Severe security level, you have the ability to allow other users who are not assigned to this document/questionnaire to access it as if they were assigned to it. As with users assigned to the document/questionnaire, where other allowed users can access the item depends on their assigned roles and the item's security level.
Select other allowed users in the same way as you select users in the Assignees step.