The "Scan To" feature of HP 7100 series all-in-one devices doesn't support Acrobat 6.

Using regedit, set registry key HKCU\Software\Adobe\Adobe Acrobat\5.0\InstallPath to the Acrobat 6 install directory (C:\Program Files\Adobe\Acrobat 6.0\Acrobat, by default).

The HP OfficeJet 7130xi all-in-one device has a "Scan to" button on the front panel that can be used to send the scanned document directly to certain applications on the attached machine. The target applications can be set in the "Scan To Settings" dialog of the HP Director software. Unfortunately, that list doesn't include Acrobat 6.

A little digging with Regmon revealed that the HP software, when populating the list of available applications, does so by scanning the registry for certain keys corresponding to known applications. If the application is found, it's listed as an option in the dialog. If the HP software doesn't know about an application then it won't be listed.

The HP software does look for the presence of Acrobat 4 or 5. For Acrobat 5, the registry key checked is HKCU\Software\Adobe\Adobe Acrobat\5.0\InstallPath. The value of this key is the path of the Acrobat 5 executable.

The HP software can be faked out by adding this key to your registry with a pointer to Acrobat 6. (The communication mechanism used between the scanner and Acrobat apparently works just as well for Acrobat 6 as for Acrobat 5.) The default installation location for Acrobat 6 is C:\Program Files\Adobe\Acrobat 6.0\Acrobat.