Finally found out why PDF's weren't viewable in IE.
Hard to believe, I know, that Microsoft updates corrupted the registry settings and disabled the PDF viewer. I just hope I'm not opening a can of worms, and discovering a large chunk of my home PC is shagged
And yes, I know, these problems wouldn't be if I used a proper browser. But since 100% of my paid work is in IE, so I get paid to puzzle over these problems, I'm not really into using anything else, yet