Just recently I started to receive the following message whenever I try to open a downloaded PDF file:
There was an error opening this document. The file is damaged and could not be repaired.
I get the same message whether I try to open the document in Preview or Adobe. I'm using Safari as my browser. I can still open PDF documents on my computer from before this problem started.
Gregg is right: the PDF that you cannot open is probably damaged. This is particularly true if you still can open other PDFs. You might want to download another copy and try again.
Interestingly enough I just went through the same sequence a few minutes ago with a page that is a PDF image. Saving the file resulted in There was an error opening this document. The file is damaged and could not be repaired.. Attempting to print the page using either Command+P or File > Print came up with a blank page. I was eventually able to print the page by using Control+Click to bring up the context menu and using Print Page from there. Save Page As… on the context menu also successfully saved the PDF image to my desktop.
I am going to have to dig into the code on the page to figure out what is going on, but at least my work around works. Hope it works for you as well.
Make intentional errors — Otherwise the Great Spirit realizes you have fulfilled your purpose on earth.