Hi there. You won't find it there because the option is available by default when you have a submitted pdf. Just go to grade a pdf assignment and you will see "launch pdf editor" underneath the assignment. See the section "Annotating PDF files" in Using Assignment
Thank you for the comment Mary. I found it
is it not suppose to be in the Feedback Types stetting too?
Anyway I thing it could be better if it would be in the "View/grade all submissions" to a quick way we can click on the "pdf annotate" and not enter to edit the grade.
maybe I will suggest that to the MDL tracker...