Hi,
you can inform your clients with a message when opening your form with an (too) old pdf reader version, to avoid problems with using the form.
put following script into the initialize event of the first page of your form!
if (typeof(app.viewerVersion) != "undefined")
if (app.viewerVersion < 8.0)
{
app.alert({cMsg:"ATTENTION:\rThis file requires Adobe Reader 8.0 or newer!",cTitle: "ATTENTION:", nIcon: 1, nType: 0} )
}