That’s rather odd, assuming that it is the correct .htm file, although every htm from the library should display something.
I’d expect it to be black if there is an issue with an error in the console 
I’m not sure what could it be specific to this PC that prevents it from displaying it.
As you said images will work, although it would be better to get to the root of them problem with .pdf on this PC.
If you’d be willing to troubleshoot it further, perhaps you could try the advanced logs - How to get a Windows Player log for advanced debugging
Maybe there will be something that could tell us more about this problem.