I know that Opus Advanced Find can find tags/keywords for all file types but from observation, Windows Advanced Search appears to only index keywords for image files.
I haven't been able to find confirmation of this limitation, assuming it is a limitation. Maybe there is a Windows option buried somewhere to enable keywords for non-image files?
You need to set up windows search for each type of file you want indexing and to tell search just how you want it indexing. You do it through the control panel indexing option.
This is a great web page about windows search:
Thanks @auden. I have been using that document as my guide. My test scenario is a folder containing a number of files including one .jpg and one .exe both tagged with asdf. The guide implies that keywords are applicable to all filetypes but if I run a keyword:asdf query only the .jpg is found and yes, .exe is definitely checked under file types in Advanced Options.
Based on my reading of the guide I also tried searching with kind:everything keywords:asdf to no avail. In fact, using kind:everything in this manner stops Windows Search from finding anything!
What am I doing wrong?
Not a lot!
I get much the same results as you. But as I have no interest in keywording exe files, I have never noticed it.
However I did discover that if I ran queries against a folder that only contained exe files, the search worked fine.
This conversation reminds me of why I have given up on Windows Advanced Search as a general purpose keyword search tool several times in the past. The Advanced Query Syntax document clearly states..
As previously reported this simply does not work. Using kind:programs on its own correctly lists all programs but kind:programs keywords:asdf does not find anything whereas kind:pics keywords:asdf works perfectly.
If a filetype doesn't have a native way of storing tags and ratings, Opus stores them in a private ADS (alternate data stream). This is the case for .exes (and also for things like .txt files which literally have no structure and nowhere to store any metadata at all within the file). If the tags are stored in a private ADS then Windows Search doesn't know about them and won't be able to search them.
Aha! That explains everything. Thanks for clarifying. Fortunately Opus knows about its own metadata so there is a way..... 
