Because Okular is build with Qt5 and the KDE Framework 5, Okular is with _little_ work cross-platform. There are nightly build available for Windows: https://binary-factory.kde.org/job/Okular_Nightly_win32/ I didn't try it, but I hear the Dolphin build (https://binary-factory.kde.org/job/Dolphin_Release_win64/) work well on Windows (just the terminal part is not available).