Not all people have a gmail account and can see office documents. Some dont know how to convert the documents into pdf. They can just send a e-mail with the documents they want to convert to convert@pdf.com and they will get pdf versions of that document.
How do you like it?
Agree with Betilfan. I've almost never run into anyone that says they don't know how to make a PDF.
If/when I have, I just direct them to a Google search or do it for them.
My gut says the avg person knows you can print to PDF and solve this issue without email.