I created a fillable form in Acrobat X.
Added a submit button
on Actions - trigger- mouse up
select action - "submit a form"
I set the link to mailto:firstname.lastname@example.org
The "PDF The complete document"
The submit works - I receive the email, but the attachment is POSTDATA.ATT.
I know I can rename the file to postdata.pdf, but my users find that unacceptable.