Okular

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Okular とは?

Okular is a universal document viewer developed by KDE. Okular works on multiple platforms, including but not limited to Linux, Windows, Mac OS X, *BSD, etc.

You can watch for development at the project Home Page.

背景

Its development began as part of Google's Summer of Code program. The description of the project can be found at KDE Developer's Corner.

Okular combines the excellent functionalities of KPDF with the versatility of supporting different kinds of documents, like PDF, Postscript, DjVu, CHM, and others.

The document format handlers page has a chart describing in more detail the supported formats and the features supported in each of them.

Annotations in Okular, which can be saved within the PDF file

As well as supporting many formats, Okular offers such features as text selection, annotation, extraction of files embedded within a document, and many other surprises. Screenshots of Okular in action can be seen here.

You can talk to developers and other users on IRC, irc.freenode.org, channel #okular.

If you are interested in contributing to Okular, please contact the team. Programmers and non-coders are welcome all the same.

Mobile Version

Okular has a mobile version since version 0.16 release in February 2013 ^[1]. The first version was based on the active framework. The mobile viewer was then ported to Kirigami in 2016 by Marco Martin^[2] and finally to Kirigami2 in 2017^[3].

The mobile version doesn't support all features from the desktop version, but provide better touch support and a mobile interface.

You can test the mobile version in your PC by entering

okularkirigami

in your terminal.

ヒント

Reviewing Documents / Annotations

Double-clicking on either one of the Review tools (F6) allows you to make multiple annotations without having to reactivate the tool after the first time.

How to keep the annotations you made to the PDF file:

By default, Okular saves annotations in the local data directory for each user. Since KDE 4.9, it's optionally possible to store them directly in a PDF file by choosing File -> Save As..., so they can be seen in other PDF viewers. Note that this feature requires Poppler 0.20 or newer for regular PDF documents. If the PDF document you are annotating is encrypted, this feature requires Poppler 0.22 or newer.

DRM

By default, Okular follow the PDF specification and don't allow copying text from DRM protected files. However, there is an option in the settings to disable DRM limitations in Settings -> General -> Program Features -> Obey DRM limitations

There was a small controversy in the Debian bug tracker a long time ago, about the default choice to Obey DRM limitations^[4]^[5]. The choice was then explained by an Okular/KPdf developer^[6].

PDF Signature and certificate

Okular can verify if a PDF certificate is valid. But you can not yet create a new signature. See release note for more information.

More Information

References

[1] Release information

[2] Commit port mobile version from plasma-framework to kirigami

[3] Commit port mobile version from kirigami to kirigami2

[4] DRM and Okular in Debian bug tracker

[5] DRM and Okular in LWM

[6] Okular, PDF and file permissions

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