Flattening converts interactive form fields and annotations into static content embedded directly in the page. The visual appearance stays the same, but the fields can no longer be edited or filled in.
Yes — uncheck any field you want to leave editable. The selected fields become static; the rest remain interactive and fillable in the output PDF.
No. Flattening is permanent — once the form fields are merged into the page content, they cannot be made interactive again. Keep a copy of the original if you may need the editable version later.