The current email system design does not provide an option for attaching documents at the moment.
What you can do in the meantime is attach your document as a hyperlink. That would require you to upload your document to some place where it is hosted and can be accessed through a web browser. For example, you could upload it to google drive and then share that link for your contact to access or view.
One benefit to doing it this way is that our system tracks opens and clicks so when your contacts click the link to view your document, you will know.