When a user clicks on the PDF icon to generate a PDF of the page, it just pops up with a completely blank, empty window.

I disabled JoomSEF and the PDFs were generated normally. So it looks like an issue with JoomSEF.

I found a forum post here asking how to avoid rewriting URLs for the PDF link:

www.artio.net/support-forums/joomsef-fre...from-being-rewritten

...which I did, but it didn't change anything.

Any ideas?

Hello,

try to switch error reporting to maximum and check your webserver logs.
Please, report back with any error you will detect.