At my previous job I was working with cliets as a support for our application. One client had problem printing invoice so they caled. Was web application so invoice was first converted to PDF then you would print it.
I ask client if they have Abobe Reader installed. Her response was some thing like that: " I don't know what are you saying. Its is like you are talking chines."
I asked for remote access, fix problem.

Still don't know how they managed to use application.