The PDF signature field is neither visible nor available on mobile phone, but works fine on a computer. Acrobat Reader has been downloaded onto the phone, and opens the pdf. All other fields are visible and working on the phone.
Just not the signature field.
Can anyone help?
Thanks for the link Bernd Alheit. But I think that answer in your link "mobile signatures is not supported" is out of date. Please observe this adobe youtube video which clearly shows the client signing on his mobile: Get documents e-signed with Acrobat DC. - YouTube
Digital certificates are not possible on mobile devices.