The WordPress.com service which hosts this website has recently hit a problem with a bug that means pdfs do not display on their sites. The pdf images can still be downloaded, and a link is supplied, but sadly no image. The developers have told me that they do not know when, and even if, the bug can be fixed!
I’m working on a way to restore the getting on for a hundred pdf images on this site, which means fiddling with some bits of code. Hopefully, normal service should be restored shortly.