Rich Text formatting in fields not working...

I have designed a certificate in InDesign and then created a PDF from this (the client wants to have an editable PDF Certificate so they can add course name, trainee, date and trainer details themselves). In the PDF I have then added Text Fields and in the Text Field Properties I have ticked 'Allow Rich Text Formatting' and 'Multi-Line' so we keep a nice script font for the trainee name etc. On the certificate itself I have put text into the fields such as 'Trainee Name here' so that they can simply over-write this with their information. I then did Save as Other' > Reader Extended PDF > Enable More Tools (Includes form fill-in & save).

I then used this PDF to test, using Adobe Reader as the client would. Whilst over-writing the text works great, the problem I have is when I copy and paste into the text fields instead (thinking the client will lift this info from somewhere else rather than hand-key the names in etc. I'm copying from Mac's TextEdit app (which is set to plain text) but when I paste into the PDF field it doesnt keep the rich text formatting that was set when I created the PDF text fields. (And of course the same happened copying from Word). Also the same happens in Acrobat too.  Using latest version of InDesign and Acrobat/Reader.

Any ideas, advice happily received. I'm stumped, have a deadline (of course) and Google isn't supplying the answers! Thank you 🙂