Typewriter
The Typewriter tool is a quick way to add some comment text to a PDF document without much editing.
Using typewriter
To select the Typewriter tool, click the Typewriter button
on the toolbar or use the Comments > Typewriter menu.
Then, click where you want to add the text comment.

You can adjust the parameters of the typewriter using the Object Inspector panel. Specifically, you can modify the following properties:
- Text format, including font (name, style, size) and alignment.
- Border line style, width and color, including background color.
Editing typewriter text
To edit a previously added Typewriter object, select the Hand Tool using the corresponding toolbar button
or press Alt+6. Then, click the Typewriter object to select it. Now, in the Object Inspector panel, you can edit parameters of the object.

Use the Visibility option in Object Inspector to adjust the Typewriter visibility on the screen and in printing.
You can also enable the Locked option, so the Typewriter object can only be modified by its author.
To modify the text of the typewriter, change colors or font, double-click the Typewriter object.

More like this:
Split and Merge PDF Files
Invisible Signature
Attaching a file as a comment
