How to annotate PDF files on Linux using Okular

Are you looking for a free app that can annotate PDF on Linux? Look nowhere, Okular should help you do that. We shall focus on its features and how to install it on Linux.

PDF files have become one of the most critical file formats for data sharing, especially the data that is not altered regularly. This includes books, brochures, documents, forms, etc. One of the most iconic features of PDF files is that they are not easily alterable. Everyone knows this, and this is why PDFs are so popular in more than half the cases.

In light of all this, there are some situations, nevertheless, when you need to make changes to or annotate PDF files. It might be because you study using a book that is saved in the PDF format, or maybe because you found a silly mistake somewhere. For this, we recommend the program Okular.

Okular Features – Annotating PDF

Being a part of the KDE project, Okular is a popular PDF annotation program, especially on the Linux platform.

First and foremost, let us check out the annotating features of this app. The types of annotations and how to use them are as shown below:

1. Pop-up Note

A pop-up note is a note that appears like just a logo of note, and when it is clicked, the whole note shows up. It stays minimized until you click it. It is ideal for making long notes is a small space.

Pop-up note
Pop-up note.

2. Inline Note

An inline note (as evident) is a note with no pop-up feature but stays there, with the text on display. It is ideal for a text string of about 17-18 characters.

Inline note
Inline note.

3. Freehand Line

A freehand line is making a line by moving the cursor around (or a pen, if you have one, and your display supports it). It is represented by a green pencil and can be used anywhere. Here’s an example (sorry for the messy lines).

Freehand line
Freehand line.

4. Highlighter

Highlighter is a straightforward feature when the tool is selected, the text that you select should be highlighted in yellow color. It should look like the following image:

Highlighter
Highlighter.

5. Straight Line

This tool draws a straight line (of yellow color) between two points that you click on the screen. The following image shows it, and it is a simple enough feature to use.

Straight line
Straight line.

6. Polygon Select

A polygon can be drawn with this tool by clicking the points between which the user wants the lines to be drawn. The lines drawn are blue on color, and it is quite a neat feature to have. This helps boxing of essential points and text or image areas in the file.

Polygon select
Polygon select.

7. Underlining

This tool is simple enough to use; when the tool is enabled, the text selected is underlined. The underlining color is black. This tool is hugely useful for any annotation made because underlining is the most used feature.

Underlining
Underlining.

8. Ellipse

When the ellipse is to be drawn, a rectangle has to be selected, and the ellipse forms inside accordingly. The ellipse is formed in blue color, and the tool is a little challenging to use. The ellipse gets drawn over the text sometimes, which is why it gets inconvenient.

Ellipse
Ellipse.

The features other than these annotations are as the following:

9. Selection tools

There are three modes of selection:

  • Area selection: The first selection tool allows users to select an area in which the options given are:
    • Text can be extracted and exported
    • Text can be used to make Okular speak it out
    • The text can be copied to the clipboard
    • Text can be searched on Google, Wikipedia, YouTube, or Yahoo. These search options can also be changed.

      Area selection
      Area selection.
  • Text selection: The cursor turns into a cursor and the text editing mode. After right-clicking the selected text, options available are to:
    • Copy text.
    • Speak the text out loud.
    • Search using different search engines.

      Text selection
      Text selection.

10. Speaker

There is an option in the ‘Tools‘ that allows the user to make Okular speak out the whole document. There is also an option to speak only the ‘current page,’ that is, the page that is in view.

11. Backends

The ‘Backends’ option provides users with the option to open documents other than PDFs to be opened using Okular. The options already available are to open MOBI files, .txt files, Open Document files, etc. Click ‘Settings can access that,’ then ‘Configure Backends.’

12. Okular configuration

Okular configurations can be accessed by clicking ‘Settings,’ then ‘Configure Okular.’ Some of the crucial options available are:

  • General
    • Toggle appearance of scrollbars
    • Toggle appearance of hints
    • Options for display in the title bar
    • Custom background-color
    • Switching to right to left reading mode
    • Opening new files in new tabs

      General configuration.
  • Presentation
    • Autoscroll advancing duration
    • Users can choose whether or not to loop after the last page
    • Toggle presence of progress indicator
    • Placement of Okular window (for a multi-monitor display)

      Presentation configuration
      Presentation configuration.
  • Annotations: This option enables users to change the color of the annotations. For example, users can change the color of the note icon, the freehand line, the underline, etc.

    Annotation options
    Annotation options.

How to use annotations

To use the available annotation tools, follow these steps:

  • Open the desired article through drag-and-drop or the ‘Open…‘ option from ‘File‘ in the toolbar.
  • Hit the F6 key, or check ‘Review‘ from ‘Tools‘ toolbar, to see the available annotation options.
  • Click ‘Reviews‘ in the left panel.

Now you can see the annotation options as in the picture below.

Annotation toolbar.
Annotation toolbar.

Installation

For Ubuntu, enter the following commands in the Terminal:

sudo apt-get install okular

Okular installation
Okular installation.

For other distributions, information can be found on this page.

Other than that, you can always install from source using these commands:

git clone git://anongit.kde.org/okular

This downloads the files to your system.

cd okular
mkdir build

This makes a directory named build, which is used for the installation.

cd build
cmake -DCMAKE_INSTALL_PREFIX=/path/to/your/install/dir ..
make install

This finally installs the program on your system.

Conclusion

Okular was created as a mere PDF viewer for KDE, but because of it being a little laggier than some other PDF viewers, this was not generally preferred by the users. On the other hand, it became extensively famous for annotations and PDF editing. We’re confident that this program should do an excellent job of whatever note-making you require. For assistance or any questions, you can always use the comments section.

Pulkit Chandak
Pulkit Chandak is a Linux enthusiast and has been using and experimenting with open source software, and hardware too since a long time. He is a huge admirer of open source software and wants to ventilate it to all around him. He is interested in reviewing and writing tutorials on Linux and its innumerable distributions. He believes that freedom in software leads to freedom of the mind from the chains of limits.

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