I recently have installed Okular on my Ubuntu 14.04.

The problem is when I open pdf files, okular gives me the error "Can not find a plugin which is able to handle the document being passed."

When I ran Okular by Terminal, this is the message I get.

okular(14100)/kdeui (KIconLoader): Error: standard icon theme "oxygen" not found! okular(14100)/kdeui (KIconLoader): Error: standard icon theme "oxygen" not found!

okular(14100) KPixmapSequence::Private::loadSequence: Invalid pixmap specified. okular(14100) KPixmapSequence::Private::loadSequence: Invalid pixmap specified. okular(14100) KPixmapSequence::frameSize: No frame loaded okular(14100) KPixmapSequence::Private::loadSequence: Invalid pixmap specified. okular(14100) KPixmapSequence::frameSize: No frame loaded okular(14100) KPixmapSequence::Private::loadSequence: Invalid pixmap specified. okular(14100) KPixmapSequence::frameSize: No frame loaded okular(14100) KPixmapSequence::Private::loadSequence: Invalid pixmap specified. okular(14100) KPixmapSequence::frameSize: No frame loaded okular(14100) KPixmapSequence::Private::loadSequence: Invalid pixmap specified. okular(14100) KPixmapSequence::frameSize: No frame loaded okular(14100) KPixmapSequence::Private::loadSequence: Invalid pixmap specified. okular(14100) KPixmapSequence::frameSize: No frame loaded okular(14100): No ksycoca4 database available!

okular(14100)/kdecore (trader) KServiceTypeTrader::defaultOffers: KServiceTypeTrader: serviceType "okular/Generator" not found okular(14100)/kdecore (KConfigSkeleton) KCoreConfigSkeleton::writeConfig: okular(14100)/kdecore (KConfigSkeleton) KCoreConfigSkeleton::writeConfig: okular(14100)/kdecore (KConfigSkeleton) KCoreConfigSkeleton::writeConfig: okular(14100)/kdecore (KConfigSkeleton) KCoreConfigSkeleton::writeConfig: okular(14100)/kdecore (KConfigSkeleton) KCoreConfigSkeleton::writeConfig: okular(14100): No ksycoca4 database available!

okular(14100)/kdecore (trader) mimeTypeSycocaServiceOffers: KMimeTypeTrader: mimeType "application/pdf" not found okular(14100): No ksycoca4 database available!

okular(14100)/kdecore (trader): KMimeTypeTrader: couldn't find service type "okular/Generator" Please ensure that the .desktop file for it is installed; then run kbuildsycoca4. okular(14100)/okular (app) Okular::Document::openDocument: No plugin for mimetype '"application/pdf"'. okular(14100): Couldn't start knotify from knotify4.desktop: "KLauncher could not be reached via D-Bus. Error when calling start_service_by_desktop_path: The name org.kde.klauncher was not provided by any .service files "

okular(14100)/kdeui (KNotification) KNotification::slotReceivedIdError: Error while contacting notify daemon "The name org.kde.knotify was not provided by any .service files"

X Error: BadWindow (invalid Window parameter) 3 Major opcode: 20 (X_GetProperty) Resource id: 0x2a0002e okular(14110) KPixmapSequence::Private::loadSequence: Invalid pixmap specified. okular(14110) KPixmapSequence::frameSize: No frame loaded okular(14110) KPixmapSequence::Private::loadSequence: Invalid pixmap specified. okular(14110) KPixmapSequence::frameSize: No frame loaded okular(14110) KPixmapSequence::Private::loadSequence: Invalid pixmap specified. okular(14110) KPixmapSequence::frameSize: No frame loaded X Error: BadWindow (invalid Window parameter) 3 Major opcode: 20 (X_GetProperty) Resource id: 0x2a0001d X Error: BadWindow (invalid Window parameter) 3 Major opcode: 20 (X_GetProperty) Resource id: 0x2a0001d

I would be much appreciated for any suggestion to solve this problem. Thanks a lot :)