It is not uncommon to have to leave notes on a submission that only administrators have access to. It is also helpful if you need to run reports.

To add an Admin Only field, load up your form builder.

Drag a field over of your choice from the left side panel.

Name the field with an appropriate label and then click Hide from Applicants and Hide from Judges checkboxes in the field settings.

When viewing the submission as an admin, the field will appear there in the form and only be viewable to you, but not to the applicant and not to the judge.