Scan to PDF issue

When I scan documents and email them to my co workers, they can't open them.  they get a message saying they have to download an add on from adobe.com.   sometimes it works for them, sometimes it doesn't   how can I get around this?

my printer is Epson Work force pro  WF-4720

I understand it is my printer causing the problem.  I need to know how to fix or which printer I can get that this won't happen?