FreePDF: Creating Interactive forms is not possible in FreePDF.
To work with forms, choose the ribbon command Insert | group Objects | Form field 
.
Adding a form field
To add a new form field, select a form field type in the menu of the command Form field (see Available form fields), and drag a rectangle in the document with the mouse.
Moving and scaling form fields
To move a form field or to resize it, first click on any form field type in the menu of the command Form field to enable form field mode. In the document, select the form field that you want to change by clicking on it with the mouse. Use the handles in the corners of the field to resize it, or move the form field with the mouse.
Changing properties of form fields
To configure a form field, make sure that a form field type is enabled in the menu of the command Form field, and then double-click on the form field that you want to configure in the document.
For more information, see the next section Properties of form fields.
Tip: Aligning form fields to the grid
To create a uniform layout for form fields, use the function "Align to the grid":
On the ribbon tab View | group View | Grid and guides 
, enable the commands Show Grid and Snap to grid. You can then let the form field objects "snap" to the lines of the grid when moving them.
Note: Grids only appear in FlexiPDF and are not visible in other PDF viewers.