by Davo Smith.
I'm not sure there is an easy way to upload the PDFs as each student (but I will await corrections from others on the forum).
However, if you just care about getting a grade into the gradebook, you could create an assignment, with no submission methods enabled (i.e. no file upload, no comments, etc.). You could then grade each of the students there (you could also turn on 'file' feedback and upload the marked PDFs as feedback). That way the grade would appear in the gradebook.