How to add attachment in mail merge with outlook for mac 2

Does anyone know how to add an attachment to a mail merge using Microsoft Office for mac 2011?

I use a 2015 MacBook Air with Yosemite.

Do I need special 3rd party software?

I have no problem doing a mail merge with a combination of Word, Excel, and Outlook.

I would like to add the same PDF attachment to this email merge.

Any help??