Cause
The file is displaying an image rather than a full PDF document. Often the result of converting the file to a PDF through unconventional methods.
If Adobe Acrobat is not set up to load large images, it will not display the contents of the document.
Resolution
1) Click the Edit menu and choose Preferences.
2) In the left-hand pane, click Page Display. Then, check the box next to "Show large images".
3) Click OK.
Outcome
The PDF file will display correctly.