I just used the digital signature thing on the mac.I am pretty sure you need a wet-ink signature (print, sign, scan, then email).
Strange that you couldn't print it. What did you open it with? If all else fails, you might be able to take a screenshot to save it, but that usually gives poor resolution.
Fill out and sign PDF forms in Preview on Mac
In Preview on your Mac, you can add text or a signature to a PDF form.
support.apple.com
Worked for my Model 3 in April just did the same for the Model Y last week