Preview displays blank page with some pdf files but prints what is hidden

Some of my pdf files have started coming up as blank in Preview. There still is data underneath, which selecting areas will disclose as though you are scraping white out off the print. Printing is unaffected, and only some files are affected. Tried repairing permissions, but no luck. I recently did the OS update, and didn't notice the problem before that. I have restarted the computer a couple times,. a few odd artifacts have shown up on the screen as well, though box selecting over these causes them to disappear. I haven't been able to find any consistent difference in the pdfs that will display properly and the ones that won't. doesn't appear to be associated with when they were created or which version of software they were created with. Saving them under a different name doesn't help. Adobe reader works fine, so it is specific to Preview ( which I would rather keep as my default reader )

Any ideas what went wrong? How to fix it?