The free version of Foxit PDF Reader lets you add a text box to your PDF files. To do this, follow the steps given below: After doing this, click anywhere on your PDF file. A text box will appear ...

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.