I'm having trouble viewing pdfs using Preview on my Mac (OS 10.4.11). Parts of the document don't show up. I usually have to close the file and reopen it several times before the entire document renders properly. Has anyone else had this problem, and were you able to fix it? And, if so, how? I should add that I tried downloading an alternate pdf viewer (Skim) to see if that would fix the problem, but it didn't. The pdfs themselves aren't bad, as they open just fine on my (Windows) laptop. They come from all different sources. As a data point, I don't notice this phenomenon on documents that are scanned from paper and then converted to pdf (like old articles).