Ghostscript itself is there. In the MoodleBox terminal:
GPL Ghostscript 9.25 (2018-09-13)
Copyright (C) 2018 Artifex Software, Inc. All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
I didn't test the PDF annotation in MoodleBox yet. I have seen that never Moodle versions use a whole lot of programs like unconv and others from OpenOffice. And also there are broken PDFs. May be you could start at the other end. Upload a PDF to MoodleBox which is known to be "annotatable" in another Moodle and go from there.