I am using Adobe Reader X on my MacBook (OS X, 10.6.8). If I have a pdf open in Reader, and then put my laptop to sleep, after it wakes up the content of the pdf is no longer visible. It's not that the window is all whited or blacked out, there is no window. There is only a menu bar. The file cannot be returned to normal by selecting it in the Window menu. After this happens, the only way to view this file is to close Reader and re-open the file. I tried reinstalling Reader X, but still have the same problem.