We have created a series of forms with fillable fields with Adobe LifeCycle 9 and we hung them on the web. Forms can be opened and filled out normally with the Adobe Reader 9 plug-in or later, but not with earlier versions. We have tried to convert the original files so that they can visualize with older versions of the Reader, but I can't, neither from the own LifeCycle nor from Acrobat X Pro.
