I notice Alfresco demo on Amazon has better preview than Alfresco Community (eg. zoom in/out, or flip to other pages). Is there a way to make Alfresco Community to have those features?
It's the exact same software. The preview functionality is identical across all editions and installations. If you are running Community locally and you aren't seeing the rich preview, it could be that you have not configured the dependencies (such as pdf2swf, ImageMagick, OpenOffice, etc.) correctly.