A student viewing annotated PDF feedback cannot navigate using the next button, but page-selection and previous buttons work.

After some digging it appears that MDL-75898 has caused a regression such that EDITOR.pagecount is not being set, and so the next button is always disabled as EDITOR.currentpage is always greater than 0 (ie EDITOR.pagecount).

I do not fully understand the intricacies, but I think the solution is to add a line to set the pagecount:

                        if (this.get('readonly') === true) {

                            this.pagecount = data.pagecount;

                            this.prepare_pages_for_display(data);

                            return;

                        }

At least this worked in my debugging.

See here: line 3796 of mod/assign/feedback/editpdf/yui/src/editor/js/editor.js

https://github.com/moodle/moodle/commit/a243d466209959437079e1e232f3fcb9aca1bdd7#diff-4471508051a0d012ff12ad2f2c96d3c1ee00d1e0fabe8e6dee2d45fb172793d9R499-R502

https://github.com/moodle/moodle/blob/a243d466209959437079e1e232f3fcb9aca1bdd7/mod/assign/feedback/editpdf/yui/src/editor/js/editor.js#L499-L502

Alternatively, should prepare_pages_for_display() set the pagecount?