I'm not sure I understand the connection between iCloud and this problem. Is it simply a problem of coincidental timing (ie, the problem happened after you set up iCloud)? If so, there's almost certainly no connection between these two events.
Where are you getting the files you're trying to open, and what specifically happens when you try to open them?
Might be true that it is only a coincidence. I open the files in my mailprogramme for Mac Microsoft Exchange. Of the PDF files I try to open in 80% of the cases Review does not open them. When opening I get the message that Preview is not ablt to ope the PDF. When I try to open JPG's it does open the file. But I am only able to see the top stroke of an image (the first 10%) the rest is grey.
Sounds like file corruption, though I'm not sure why that would be happening. If it's only happening with files recieved as attachments from an Exchange server, I'd be inclined to blame the server. It couldn't hurt to repair your hard drive, though. Hold down command-R at startup, and the use Disk Utility to repair the hard drive.