1- using the attachments tab
I have included the PDF which allows the user to add attachment , view the attachment and deleted the selected attachment from the form.
Please click here to access the formPDF Form
PS- THIS WILL ONLY WORK WHEN YOU OPEN THE FORM WITH ACROBAT.IF YOU WANT IT TO WORK IN READER YOU WILL NEED TO APPLY USAGE RIGHTS USING THE READER EXTENSIONS ON THE SERVER
Original article at http://eslifeline.wordpress.com/2009/04/06/adding-attachments-to-pdf-form/.