Open your PDF Marker and click on the 4th icon 'Upload PDF file(s)

Select (on the drop down list) the working folder for your assignment. When you click,

On the  rubric selection, please leave it on 'No Rubric'

Enter the correct credentials for that student.

Browse the submission file for that student. You click on 'Browse' to be able to add the file.

When you are done, the 'Submit' should have turned to purple and you click on it.

The submission should appear like this and you will be able to mark

This guide will help you to upload single assignments to PDF Marker.

How to upload a single assignment to PDF Marker