Adding text fields and other form elements to create editable PDF forms in Adobe Acrobat Professional XI is a straightforward process. These elements create an interactive document that is ...

As you fill out your form, you may need to add instructions or other text in spaces where no field is provided. You can use the same text cursor, click on any space on the form, and type.

Adobe describes an alternative approach to changing the font size in a PDF that works on Acrobat 2017, 2020 and DC. It changes the default font for "Add Text" and general text editing features.