I would like to fax from my Mac running High Sierra
Assuming you don't want to upgrade your printer, buy/borrow a fax machine or pay for an online service, then the only remaining options are:


print the pages and take them somewhere to fax for you
find an online fax service with a free trial period
use a fax modem1 if you happen to have an old one laying around


If this is a once off I would just print the pages and take them to your workplace or a local post office (or anywhere that has a fax machine) and ask if they can fax them for you. Even if they charge a couple of dollars, this is probably the best option.

Otherwise you should be able to find an online fax service with a free trial period. I just did a quick search and found that https://en.efax.com offers a 30 day trial period. No doubt you will need to provide payment details as part of the registration, but typically with these types of services you can just contact them and cancel your account prior to the trial period ending.

1. macOS Sierra doesn't natively support fax modems but there used to be a range of 3rd party fax programs, so you could use one of these. Or maybe just use another computer or install El Capitan on a virtual machine to do this. Or, if you happen to have Windows installed (either via Bootcamp or a virtual machine), that should do the trick too.