The improved support for .docx, .xlsx, .pptx, and package file formats only applies to new documents (or newly synced documents). For the improved support to take effect for existing documents, you will need to add or sync them to DEVONthink To Go again.
The best way to make sure documents are re-synced is to delete the database containing the documents from DEVONthink To Go and sync it again. If that isn’t sufficient (or the documents are in the Global Inbox), you’ll have to go to Settings.app and reset DEVONthink To Go from there. I hope to fix this in the next update, but if your device supports multitasking, you’ll have to completely quit DEVONthink To Go before the Reset takes effect.
Finally, package file formats sent to DEVONthink To Go from another app (such as an email attachment) are not currently handled correctly. I am working to fix this right now, but for now the best way to get a package file format into DEVONthink To Go is to sync with DT.