Should Online Processes Assume that the User has Access to a Printer?

No.

At first I thought you might assume there is a printer if the process is specifically for owners of a (working) printer. But then I realized that the user of your process/website is not necessarily the person who wants to print. So that's a no.

@Sujit suggested user research. You should definitely do that. But: just because the users in your research might all have printers, it doesn't mean all your potential users might have them. So that's also a no.

You should ask your boss if you can afford to miss even one user because of a missing printer. The answer will most likely be no.

If your process is for a public institution. That's definitely a no. You legally can't exclude anyone from your process. While your whole page might be accessible for blind users, the printed document will not. So no again.

What about competition. The ease of use is very important. If your compete for example with UPS or FedEx you can not afford to have a more complex process. Sometimes users might not have an other option than to use your process. Like online shopping returns. The shop decides how you return the product. If the user is forced to use your process she might hate it. She will hate your process, your product, your company and the shop that works with your company. Definitely a no.

It is always extra work to print, even if you have access to a printer. Just spare them this work.

Google recently stated that more people are using the internet on mobile now than desktop devices. Therefore, it's likely more people do NOT have immediate access to a printer--though that does not mean no access.

That said, one can never assume anything on the internet including the possibility that I might be a dog.

I believe insight for printing should arrive from the user study and identifying the user need. You could also research on the context of the user.

If you have sufficient evidence, your user needs to take output of some artefact, then you could brainstorm whether it could be download to PDF or save as image or print.

Ultimately, I suggest we do not assume, but base our features on user research.

Thanks, Sujit