In other words, Adobe Reader won't let you add text. What you need is a program that's a little more accommodating, PDF-wise. Try Foxit Reader 4.3, which allows you to add text to any PDF.

To change the default PDF viewer on Windows 10, you'll need to edit your default apps in the Control Panel.

You can add text to an iMovie on an iPhone, iPad, or Mac. There are more precise editing options available with the Mac software.