extract xml data from pdf form

Hello,

what are the conditions to be able to extract data from a pdf form ? I have thought, that it is required to have XML Schema data connection and that all the form fields must be bind to this data connection.

But today I found, that the fields can use just "Use name (FieldName)" connection, that is something default - and no explicit data connection is therefor needed.

What is the common approach for designing forms, that should be extracted by LC processFormSubmission ?

Thanks.