When a teacher creates a document and the student downloads it and saves it as a pdf, then the student adds text comments to the PDF document and adds text boxes and saves it, when the file is uploaded to the course, the assignment grader does not render the document. It just displays the original document. It has to be downloaded in order for the document comments to be viewed.
STEPS TO REPLICATE
1. Create a PDF document.
2. Add mutiple text boxes to the saved PDF document
3. Save the PDF with the text boxes
4. Log on to Moodle site as a student
5. Upload the PDF as assignment submission
6. Log out of the site as the student
7 Log into the Moodle site as teacher or admin
8. Navigate to the assignment
9. Click grade
10. View the submitted assignment. The pdf document does not render
11. Download the assignment and you can see the pdf with the comments inside of it.
When I download form I notice that there are multiple text boxes on the PDF. Here is an example https://www.screencast.com/t/sJ5nxfb8SuWr. So it looks the student took a text document that was given by the teacher, saved it as a PDF document. Then to fill out the PDF document, the student created text boxes via comments for each of the fields to enter the answers on the form. And when the teacher tries to grade the form it does not render the text boxes in the PDF grader screen.
However it looks like if the student filled in the text document before saving it as a PDF document then the answers do show in PDF grader without having to download the document.
The pdf document should still render in the assignment grader. It should not have to be downloaded to be graded.
I tested and created a brand new pdf with additional text added and it worked. I compared the original pdf used in testing as a student submission and I believe the difference is that the pdf had markup/comments added to it not actual textboxes.
I can't find any hard documentation, but I suspect that unoconv and the inline viewer don't display the added pdf markings/comments.
When this scenario occurs it has to be downloaded in order for the teacher to grade the assignment.
ATTACHMENT / LINK Sample pdf document with the student data entered for testing where the comments only show up if downloaded:https://drive.google.com/file/d/1VdBZKDBJbvINuePqifoGq1rs35HqGaQN/view?usp=sharing
Another test pdf document that was created in word, then saved as a pdf, the student added true text boxes (not just comments), and then it was resaved as a pdf and did display inline with the additional comments