Attach document in email

I am developing a website and I need the form to have the option to send an attachment. I do not find the option or if someone knows how to do it.

Thank you very much
Excuse my English I use a translator

Is it somehow possible to send a file as an attachment in the form with little effort.
for html I have already inserted only in php programming I fail.

Does anyone have an idea or an example?

As it looks like, there is no solution here at the moment. Would still be interesting if someone finds a solution.