Font issues when sending PDF for signature

I have created a form using Acrobat Pro DC adding in all of the content text as well as various check-boxes, text input fields and radial buttons. All looks fine... that is until I try and send it to be completed and signed. The fonts go absolutely crazy and the letter spacing is completely bonkers... HELP!

From this:

To this:

I have tried changing the font to ARIAL but this issue continues

Any help will be gratefully received!