If you are receiving an error when trying to save a PDF document then it may be due to a setting in adobe acrobat reader. An example error message is below. To fix it a preference needs to be adjusted in acrobat reader and a screenshot with instructions is below.
Example error message
In Acrobat Reader menu go to Edit -> Preferences -> Then un-check the "Save as optimizes for Fast Web View"
You can have your contractor create a Timogix account of their own and they can then create an invoice from there.