Without an extension you will probably need to just export the visualization to pdf or image and then attach to an email manually.
As stated above you could email them the entire app. But then they would have to have QS installed and know what to do with the file. But that doesn't sound like what you are asking to do.
If you have requirements for formatted reports then your best bet is to have Qlik Sense Enterprise with NPrinting. But that involves cost.
Check Qlik Branch. I don't really see anything there. But something might jump out at you depending on what you need.
Remember that Desktop is just a personal version and is not intended to have all of the functionality that a production Qlik Sense installation would have.