Can't see my books on the PC

I recently got a Boox go. 10.3. I currently use it for school and have school books on it that I take notes in. These books are in PDF format. However, when I want to view the books on my PC, I can't click on them/view them. This is not possible in send2 boox and not in booxdrop.
I don't know if I'm missing something that prevents me from opening the books on my PC. I have turned on synchronization and am on the same account.

How can I open books that I have made notes in on my boox on my laptop?