Hey frostfree,
Thank you for reaching out! This is outside of our scope of support. However, based on my personal experience, to send a fax via a file, you will need a dial-up fax modem on your computer to connect to a phone line. Once you have that, on a Windows computer, you can click the Windows button > Device and Printers > Fax > select your file to send > input phone number.
Hope that helps!
Cheers, Tony | Community Mod.
