“clipboard-copy / save their own data as plain text” is possible with the Views function in Formidable Forms. This plugin strictly merges Formidable Form fields to PDF form fields.
However, “reusing that text is to copy all the text to clipboard and paste into new (unfilled) form with one click. Is this possible?“, no we don’t think so… anywhere, with any web form tool – but sounds like a useful idea – let us know if you find something.
We remain at your service, regarding dynamic pdf forms from WordPress forms, using Formidable Forms.