I had to do exactly that recently when I needed to send a signed freelance contract. The process is surprisingly simple now — you can scan your signature or document, upload it to a fax app, and send it right away. I found a useful step-by-step tutorial on https://derekdubois.net/ that explains how Android users can send legal documents securely. It even mentioned which apps include encryption for privacy. I tried one of the recommendations and sent my contract while sitting at home. The client received it within minutes. Faxing from a phone might sound strange, but it works flawlessly once you set it up.