I’ve uploaded a PDF file as evidence into my students Markbook but it’s not showing on the report. What have i done wrong?

Only image files such as .jpeg or .png files can be uploaded into the Assessment Markbooks. 

The quickest way is to take a snip of the document, save this somewhere on your computer and then upload file in thre Markbook.  Alternatively, you could take a photo of the PDF, save this and then upload.