SUMMARY I wish Okular could have a stable release for win7. Okular's stable version is available on the Microsoft Store, but win7 can not use Microsoft Store and I can't find a download link for Okular's stable version in win7.
Windows 7 is no longer even supported by Microsoft. It doesn't seem reasonable for KDE to do it. :) If you can't bear to leave Windows 7 (the best version of Windows, after all) because 8 and 10 seem like downgrades, might I recommend you try a Linux distro with KDE Plasma? I'm partial to Fedora KDE myself, but you can see some other recommended options at https://kde.org/distributions/.
Windows releases are also available on https://binary-factory.kde.org/job/Okular_Release_win64/, but I'm not sure if they'll 100% work with Windows 7