FreePDF: Creating interactive forms is not possible in FreePDF.
FreePDF enables you to complete forms. The commercial version FlexiPDF also allows you to create your own forms with interactive buttons, checkboxes and other form objects.
These new forms can then be completed with FlexiPDF, FreePDF or another PDF viewer. The form values can be exported with FlexiPDF to XML format for further processing.
Completing existing interactive forms
To complete an existing interactive form, enable the Hand tool 
and then click on the fields in the form.
Creating your own interactive forms (not available in FreePDF)
You will learn how to create interactive forms in the following sections: