Your instructions to allow quickview for odt documents involve installing Open Office and it's optional ActiveX component.
However since LibreOffice is a branch of Open Office and is cited as being better maintained and supported I installed that instead.
Despite including its ActiveX component, odt files would not appear in the DOpus quickview window. This is not a big problem, because after I installed Open Office, odt quickview immediately started working, and I can still continue using LibreOffice as before. However, I'm curious if you have heard about this problem before and if there is a way to get quickview to work without Open Office.
Sometimes I save a file in doc format instead of odt format, and so I also would like quickview to work with doc files. I followed the instructions to add the ".doc" extension to the list of extensions under "Internet Explorer 32-bit" under "ActiveX+Preview+Office+Web Plugin Configuration", however when I try to enable quickview on a doc file, the file does not appear in the quickview window. Instead I get a popup window asking me if I would like to open or save this file.
It may not be relevant, but in my experimentation, I tried removing the ".odt" extension from the list (under internet expl. 32-bit) expecting that quick view for odt files would no longer work. However it worked just as good as before except that after the file name in the header it said "SOActiveX class" instead of "Internet Explorer 32-bit".
QuickView (Plus) is a specific 3rd party viewer package sold by AvantStar, which works with Explorer and Opus and can view lots of document formats. It shouldn't be used as a generic name for any other viewer or the viewer pane itself, as they're different things. It sounds like it not involved here.
It sounds like your versions/combinations of Open Office & LibreOffice do not include a viewer which works in current versions of Internet Explorer, but do include an ActiveX control viewer that works via the Generic ActiveX route. The difference is just in how the controls are hosted within the Opus viewer window; some controls work better if Internet Explorer is sandwiched between them and Opus, while others work better directly.
Both are somewhat legacy ways of displaying files, with the more preferred method being Preview Handlers, which we also support. I'm not sure if any of the Open Office forks have a preview handler yet, but if they do then you'd also see it work within Windows Explorer / File Explorer's viewer.
I have no idea if this actually helps (I really need to install one of those office suites at home), but I'm curious if the last link on this page will work:
I think of the DOpus preview pane as a "quick view" but I see now I shouldn't have called it that. But you guessed correctly that I hadn't installed quick view plus, although that does sound like it would be a good solution (except for the fact that I would have to buy it).
I'm not sure if any of the Open Office forks have a preview handler yet
I appears to be recognized that Open Office and Libre Office should have a preview handler, but it sounds like it is not a trivial task to add one, so I'm not optimistic that they will have this soon. In the mean time, at least the legacy method (ActiveX) works well for ODT files. I'm confused that it doesn't work with DOC files too since I wouldn't expect that open office would handle it that much differently. Plus I vaguely remember getting that to work once before, probably with older versions of Dopus and/or open office. So possibly I'm still doing something wrong.
Another solution I'm considering is to convert all my DOC files to ODT format. I had been avoiding that in case I wanted to share one of my documents with a microsoft office user. However I've recently learned that since 2007 microsoft office has also supported ODT, so perhaps there is no longer a valid reason to keep the DOC format around.