pdf.js–as I understand what google gave me–is used to display a PDF in the users browser. As go is run on the server, you can not make it display anything in the users browser unless you want to re-render the PDF as HTML and send that (along with embedded media) back to the user.
Most modern browsers are able to render PDFs on their own today, therefore I’d just send the PDF to the client and let them choose how to view them.
This way, its the users responsibility to use the tools they are comfortable with and they feel safe to use.