Hi,
They are not defined in the DarkMart, because simply those buttons are completely useless and gives nothing but problems.
"PDF" button = Joomla is not good to generate PDF version of web page, lots of space and margins generated, 3rd party PDF plugin is required.
"Print" button = useless again, people can print page by clicking the CTRL+P button.
"Recommend to Friend" = Since the "sender" email is external, most of the time this email goes to SPAM folder directly.
But i am writing down your request, no big deal and your request will be taken into account in the next release of DarkMart.
Regards.