Send PDF by email in HTML format

Hello, 

I would like to set up a Java button on my PDF file to send it by email. But I can't find how to set up the mail in HTML format.  I'm using the following java code :

var fObject = "..."

var fMsg = "..."

this.mailDoc({cTo: "...", cSubject : fObject, cMsg: fMsg})

What should I use to set up the mail format in HTML ?
Thanks a lot in advance !!

Christophe