Page size is too small - part of page is cut off

When I try to open an old document from 2019, part of the page is cut off. First, I thought that someone exported the pdf in a wrong format. However, when I edit the page, I can see that the rest of the page is still there (see screenshot). 

Do you guys know how I can restore the rest of the page? Changing the orientation or page size in the printing options didn't work for me. I tried looking for forum entries with similar problems as well, but it seems that mostly this problem arises when printing. But as you can see, this problem also also applies when viewing the document.

Thanks for all help!