Okular showing a PDF in KDE SC 4
|Developer(s)||The Okular Team|
|Stable release||0.16 / February 6, 2013|
|Operating system||Linux, Unix-like, Windows, Mac OS X|
|Type||Universal document viewer|
|License||GNU General Public License|
Okular is the document viewer for KDE SC 4 (although it does not require the full KDE desktop). It is based on KPDF and it replaced KPDF, KGhostView, KFax, KFaxview and KDVI in KDE 4. Its functionality can be easily embedded in other applications.
Okular was identified as a success story of the 2007 Season of Usability. In this season the Okular toolbar mockup was created based on an analysis of other popular document viewers and a usage survey.
Okular's annotation features include commenting on PDF documents, highlighting and drawing lines, geometric shapes, adding textboxes, and stamps. Annotations are stored separately from the unmodified PDF file, or (since version 0.15 with Poppler 0.20) can be saved in the document as standard PDF annotations.
Text can be extracted to a text file. It is possible to select parts of the document and copy the text or image to the clipboard. Other features include trimming of white page borders and setting of bookmarks.
File format support 
It supports the following file formats:
- Portable Document Format (PDF) with the Poppler backend
- PostScript with the libspectre backend
- Tagged Image File Format (TIFF) with the libTIFF backend
- Microsoft Compiled HTML Help (CHM) with the libCHM backend
- DjVu with the DjVuLibre backend
- Device independent file format (DVI)
- XML Paper Specification (XPS)
- OpenDocument format (ODF) (only odt)
- Various image formats
The official version obeys the DRM restrictions of PDF files by default, which may prevent copying, printing, or converting some PDF files. This can be turned off in the options under "Obey DRM limitations", however.
See also 
- KDE Developer's Corner - Google Summer of Code 2005 Projects
- KDE Developer's Corner - Okular
- Season of Usability Published on September 30th, 2007 by Ellen Reitmayr » Okular
- "Bug 151614 - store annotations with documents".
- Okular - Document format handlers status
- Okular and DRM
- Okular, PDF and file permissions
- Okular, Debian, and copy restrictions
- Debian Bug report logs - #531221 okular: Arbitrarily enforces DRM by default