Can't open uploaded pdf

(this is what my flashcard shown, only provide the page information but don’t show the image of the pdf)

I’m using my macbook to study, i don’t know why that i can’t open the uploaded documents. Some of my friends also use memo with ipad, the flashcard they generated has provided the exact page and the image of the uploaded document that relate to the specific flashcard. However, my macbook doesn’t show it. I hope you can fix it.