When a student uploads a PDF document which has been annotated outside Moodle (e.g. with MS Edge or Drawboard PDF), Moodle's built-in PDF annotator sometimes displays a blank page (Moodle 3.7), sometimes the original document without annotations by the student (Moodle 3.9).

To reproduce, you can use the attached document annotated_pdf.pdf, which was annotated with MS Edge (you can open it with a PDF reader it to verify that it contains annotations) :

1. create an assignment with "File submissions" as submission type
2. as a student, submit the attached document
3. as a teacher, verify in the pdf annotating page that the submission is blank or doesn't contain the student's annotations.

This can lead to serious problems, especially now that tablets/convertibles with touch screens become more common. Consider an assignment where the teacher asks the students to annotate a specific document on their computers, and to upload it back into Moodle. if the submission displays blank, the teacher might infer that there is a problem with the pdf file. But if the document appears without the student's annotations, the teacher might just think that the student has not done his/her work.

Currently, the workarounds are :

• ask the student to generate a "flat" pdf, e.g. by printing it as a pdf, or using the software functions (e.g. Drawboard PDF: How to flatten form fields and annotations)
• the teacher annotates the submissions outside Moodle