The document interface on Windows was changed in Acrobat 8 to a single document interface (SDI) which displays each document in a single top-level floating window.

Redax will only function in the multiple document interface (MDI) which can be re-enabled via the preferences panel. Change the preferences by:

1. Start Acrobat.
2. Choose Edit -> Preferences
3. Choose “Documents” from the column on the left side of the dialog window.
4. At the top of the Open Settings, uncheck “Show each document in its own window (requires restart).”
5. Close and restart Acrobat.