It’s not very uncommon that we might need to merge different PDF’s or images into one PDF in our daily task. So in this article we learn about a very powerful command line tool called ImageMagick and learn how to use it.

Installing ImageMagick through apt

ImageMagick comes preinstalled in Ubuntu 20.04 as there are many package that use this tool as a dependency.

Installing ImageMagick through apt (Advanced Package Tool) is pretty straightforward. The package is already available in standard Ubuntu repository

Open the terminal and execute the following:

  • First refresh your local package index by executing:

    sudo apt update

  • Next execute the following command to install ImageMagick:

    sudo apt install imagemagick

Using ImageMagick to merge multiple images into one PDF

We will use the convert command line tool of ImageMagick to merge multiple images into PDF.

To convert use the following command:

convert image1.jpg image2.png image3.bmp output.pdf

The order of images in the command determines the order in which images are merged in the output.pdf.

If you get the following error while converting to PDF:

convert: attempt to perform an operation not allowed by the security policy 'PDF' @ error/constitute.c/IsCoderAuthorized/408

Jump to Solving the Security Policy Error section where we have discussed how to solve this issue.

Using ImageMagick to merge multiple PDF into one PDF

We will use similar command that we used before but with some extra options so that quality of the output.pdf is good.

To convert use the following command:

convert -density 300 file1.pdf file2.pdf file3.pdf output.pdf

-density sets the dpi that the PDF is rendered at. Setting this to 300/600 will give a fairly good output.

You can also use image and pdf interchangeably in this command which makes it even more powerful. That is :

convert file1.pdf image1.jpg output.pdf

If you get the following error while converting to PDF:

convert: attempt to perform an operation not allowed by the security policy 'PDF' @ error/constitute.c/IsCoderAuthorized/408

Jump into the next-section of this article to solve this error.

Solving the Security Policy Error

ImageMagick has some security policies disabling some rights for security reasons. You will have to edit a config file to re-enble the action you need.

Open /etc/ImageMagick-6/policy.xml with your favorite text editor, find the line
<policy domain="coder" rights="none" pattern="PDF" /> and replace none by read|write”

Step By Step Process to achieve the things mentioned above

Open the file in terminal and execute:

sudo nano /etc/ImageMagick-6/policy.xml

Find and edit the line:

<policy domain="coder" rights="none" pattern="PDF" />

to :

<policy domain="coder" rights="read|write" pattern="PDF" />

References: AskUbuntu

After performing the task I would recommend to change the policy.xml back to what it was before. There are many other useful tasks that can be performed using ImageMagick such as resizing images, converting between image formats and many more but that we would cover in some other article.

I hope this article helped you to merge multiple PDF/images into one PDF in Ubuntu Linux. Questions, suggestions, a word of thanks is always encouraged.