In short it is not safe to keep private and confidential stuff in Gmail or other document provided by Google. Despite they are keen and aware of the trust that you place in them. As part of their responsibilities. The information collected will be used for their newly enhances products and services.
In this way Google make their money by recognizing a lot about you. So as they can allow other companies to easily direct advertise to you.
Please read more about their ‘Transparency and Choice’ in their ‘Privacy Center’. You can choose whether or not to share your documents.
