Hi, I have created a fillable form, which could be resend by clicking a special sign (action: relase the mouse button -> send the whole PDF form to a special e-mail account). As others and myself tested it, everything was fine (using Adobe Acrobat Pro DC or Reader DC in a Windows based system).
Now, one tried it with Mac (he used a pre-installed PDF-reader - I do not know which exactly): Everytime he clicks on the sign, the file is going to be closed and the form won't be send. What is the problem?
You must INSIST users use Reader - and tell them they must not use iOS or Android too. Mac comes with "Preview" which not only does not understand forms, it destroys them. You will need to provide tech support to your users, as many will not have Reader at all, and will be reluctant to download it too.
PDF forms need to be viewed with Acrobat or Reader to work properly, any other viewer may not work (such as Mac Preview). You can add a message to the first page of your PDF that would only appear if the PDF were opened on a non-compliant viewer, here is a related discussion: