downloading a file, and opening a popup

I got a button, and I want it to do 2 things when the users click on it :

1- download a file.
2- open a popup with some content in it.

for (1), I got a simple avia-button, with the href pointing to the file.
for (2), the following tip from Ismael was perfect to get a popup :

https://kriesi.at/support/topic/contact-form-in-pop-up-prettyphoto-issue/#post-304173

but the problem is that it takes its content from a href.
So I don’t know how I could do both actions from a single button.
any good way to handle that with enfold?

perhaps I use ‘onClick’ in some way to download the file ?
any idea?

many thanks!
Charles