To pass hidden value to after the next page

I'm stduing contact form useing this gentleman's code.

Contact form URL

This contact form has confrim page. I would like to display some value at final page with "Thank you your message has been sent" message.

Is it safe to send the value to after next page? I'm okay to show the value. Could someone teach me how to pass the value after next page? I appreciate that if you show me how to write code.

via Chebli Mohamed