If you right click an existing form field, and select Properties from the drop down (or click the PROPERTIES OF SELECTED button when selecting a single form field), the above dialog will appear.

You can’t change the form field properties of an existing form field, without first converting it to a style which PDFtypewriter can more easily read and manipulate.   To do this, click the CONVERT TO EDITABLE FORM FIELD and the form field will be converted from the pre-existing format to a more readable and malleable format for use in PDFtypewriter.

Note: If the form fields are tied by JavaScript or validation scripts, you may not want to convert to editable, as this may cause the pre-existing JavaScript to not work.   PDFtypewriter does its best to preserve the JavaScript and validation scripts, but as with any conversion process, it is not always perfect.