Problem changing "Launch by default" setting


Dec 21, 2011
I recently bought an A1CS 220 tablet.
When I first tried to read a pdf file, it asked me which app to use. I selected Quick Office & set it to always open with this. I noted at the time that I could change this setting by going into application settings.
Iwasn't over enamoured with the way the app displayed pdfs & since I'd already installed the Perfect Viewer app for reading cbr/cbz files, I decided to get the Perfect Viewer plugin for pdf files.
I like it much better, especially since it uses the volume up/down buttons to turn the pages.
So, I went into Application settings & selected Quick Office & there's nothing in the "Launch by default" box to delete. Can't find anything else that helps. How do I change this setting?