I want to view Qt reference documentation inside QtAssistant, but the installation of Qt5 did not come with .qch documentation files for Qt libraries.
I have tried to fi
Yes, the official Ubuntu-documentation for Qt5 is very incomplete. You don't have information about nearly any class.
If you want to use the QtCreator/QtAssistant build from Ubuntu you have to acquire the docs yourself. I did and uploaded these on my personal Mega-account. Here are the docs. I installed the Qt framework with the installer from qt-project.org, grabbed the documentation and inserted it into the software-center-version.
I don't use QtAssistant as a stand-alone program but integrated in QtCreator. To add the docs to QtCreator go to Tools>Options>Help>Documentation and click add. Then select all .qch files, click apply and enjoy. Maybe try the way as mentioned above.