Need to edit a PDF document but don’t want to pay for the more expensive Adobe editors? You can add text to and sign a PDF with just the free Reader program.

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 ...

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.

Need to add text to a PDF that doesn't support editing? No problem -- and no extra software required.