I have Adbobe X Pro and I am creating a fillable form. I want to be able to add a box that allows the Adobe reader user to add an additional line or activity to the report. I have been trying to search for this but can't find it. Any help is greatly appreciated.
You'll need to use LiveCycle Designer to create this type of functionality. LiveCycle Designer ships with Acrobat X Pro for Windows. Please take a look at this tutorial for more info: http://acrobatusers.com/tutorials/creating-expanding-form-fields
David is talking about an interactive form that would create the box if requested or such. If you just want to add another field, that can be done with the standard field tools. However, it does sound like the interactive nature is what you are asking about and that would require Designer as suggested. For more help there, you might want to ask further questions in the LiveCycle forum.