Add Paperclip style icon attached file link to PDF

I am strugglin to add an Icon that i can click on with a link that opens up an attached file on my PDF - it seems like it should be simple! I recently had this working so i could double click the coloured icon on the PDF and it opened up the attached pdf i had designated - now i can't find a way to do this. I dont want a hyperlink btw, just the displayed customisable coloured icon (you can select it to be a paperclip, tab or a couple other icons in the properties when you set ip up) - it was such a nice feature for my work and now i literally cant find a way to add to the PDF - please help thanks