Xournal is a small free software application that allows you to take notes or make sketches in pdf files. This program has a graphical interface based on the GTK libraries. The interface of this program has a simple and intuitive toolbar with which to you will immediately be able to annotate your pdf files.
When the needs about a document involve changing the text, adding or removing pages from it, it is better to resort to a pdf editor more complete. When what is needed is to make annotations, add images or attach sketches on pdf files, using this small program is a very fast and comfortable option.
Install Xournal
Installing this program in Ubuntu is as simple as just opening a console and typing the following in it:
sudo apt install xournal
Besides being in the Ubuntu repositories, Xournal can also be found in the ArchLinux AUR repositories.
Once installed you will see that its interface is very basic, but effective. Xournal has a series of tools such as: the pencil, the eraser, the highlighter, adding text layers, selecting and inserting images and many others that you can discover after installation. I want to clarify that Xournal does not allow editing the text of the pdf. It does not allow it because it considers it a fund. What it will allow you to do is edit your annotations that are made on the file.
In the toolbar that incorporates in its upper part you can find everything you need to make annotations in pdfs. If you browse the program menus a bit, you will discover how easy it is to work with. To save the changes, you just have to go to the File tab and export the modified document as PDF.
Uninstall Xournal
If you are not convinced by the program, uninstalling this software is as easy as installing it. From the terminal you just have to write the following and that's it:
sudo apt remove xournal
I know that there are many pdf editors that perform tasks of this style. This program has a very comfortable learning curve. This is something very advantageous especially for those who do not have much time to stop to learn the operation of a program. Now it is only a matter of each person looking for the one that best suits their needs.