Some Pdf files won't open in Adobe Acrobat X1. I get black x in upper left corner.
I assume that this is in a web browser. Take a look at these troubleshooting tips: http://helpx.adobe.com/acrobat/kb/cant-view-pdf-web.html
If none of these work, please let us know more about your setup: Which operating system, browser, ...
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...