Add 2 sections and one text field (we'll call it "submitted") to your form
template. You do not need to show the "submitted" field to the user, so
delete it from the view (it will remain in the main Data Source of the form
template). Put the controls that should appear before the form is submitted
on the first section. Put the controls that should appear after the form is
submitted on the second section. Add conditonal formatting on the first
section: Double-click on the section to open its Properties dialog box, click
"Display" tab, click "Conditional Formatting" button. On the Conditional
formatting dialog box, add a condition that says: if "submitted is not
blank", "Hide this control". Do the same for the second section with a
condition that says: if "submitted is blank", "Hide this control". Enable the
form to be submitted. Add a rule to submit the form. This rule must have two
actions: "Set a field's value: submitted = "true"" and "Submit using a data
connection: <Your SharePoint submit connection>".

When the form opens, the first section will be shown and the second section
hidden.
When the form is submitted, the "submitted" field will be filled with the
text "true", the first section will be hidden, and the second section will be
shown. No programming required!
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S.Y.M. Wong-A-Ton