Let me be more clear and explicit on how everything work together.
Alfresco Android Application can't open any file. It needs 3rd party application to open files. it works nearly the same as windows works. You need the application/software to open a specific file type. If you don't have this application it's not possible to open it.
Alfresco Android Application used what's called "Intent" to list applications able to open the file user has selected.
If there's applications inside the device, we display the list of application and the user can select is favorite application to open/edit the file. If not application, the application display an error message.
Let's focus on office document application now.
In Android application world, I distinct 3 kinds of application : "Viewer" / "Editor" / "Integrated Application"
<ul><li>"Viewer" office application are generally "lite" version or simple dedicated application. Their goal is only to view the document. You have to paid generally the "pro" version to be able to open the file in edit mode. It generally accept that a 3rd party application (like Alfresco Mobile) send a document to them to open it.</li>
<li>"Editor" : Allows the user to edit the file. It generally accept that a 3rd party application (like Alfresco Mobile) send a document to them to open it. User can modify, save it and Alfresco Mobile will "save it back" to Alfresco Server.</li>
<li>"Integrated Application" : Allows the user to edit the file. It generally accept that a 3rd party application (like Alfresco Mobile) send a document to them to open it but doesn't enable the "save back". Why ? There's a lot of reasons it can be for example to avoid the danger to corrupt the file during the save operation or to promote their internal storage system.</li>
Google QuickOffice (V6.x) is an Integrated Application. It's possible via Alfresco Mobile to send a document to open it but not to edit it. But if you goes from inside the QuickOffice Application to the folder where your document is it can open/edit/save it. It's the choice of the application.
Before that QuickOffice (V5.x) was a viewer/editor application with a free (read only) & pro (read/write) version that worked well with Alfresco. This is the one I mentioned in my previous version.
So if you look at an application to edit office document, you have to look more on other office suite like OfficeSuite, KingsoftOffice, PolarisOffice…