Problem opening some PDF files in Adobe Acrobat

I have several PDF files that cannot be open in Adobe Acrobat.  I have the message as shown below:

There was an error opening this document. The file is damaged and could not be repaired.

But I first discovered the problem in Adobe Reader: the files cannot be open in neither Adobe Reader 9, X nor XI, in Win7 64-bit as well as Windows Server 2008 R2.  The original post in Adobe Reader forum is in this link: http://forums.adobe.com/message/6163936

BUT the files are NOT damaged because I can open them with another software called XChange PDF Viewer.

Where can I file a bug to Adobe so they can fix the bug?

Thanks in advance.