How to Use Rich Text Formatting in an Editable PDF File
When creating a fillable PDF, you can enable RTF formatting for the editable text fields.

Unfortunately, the formatting controls don’t show up by default, so it’s not easy for the user to find out that additional options are available. In fact, the user has to press ctrl + E with an editable field selected in order for the controls to pop up.
I recommend noting this shortcut in your instructions to make sure your readers don’t miss out.

Once the Form Field Text Properties dialog is open, it provides many extra formatting options that can come in handy for special use cases.
For example, you can change the font, font size, font style, color, and more.

There are also alignment options, spacing options,

and the user can even add their own link to editable fields!

