Headers & Footers
Can I use headers and footers in my mail merge?
From the Google Docs Add-on Only
You can add static text and images to the header and footer as normal in your Google Docs template.
However, text or image merge fields should only be added to the body of the Google Docs template, and not to header or footer.
Static Image in Header
Image Merge Field in Header
When merging to letters, merging content from the header and footer is only supported when merging to multiple documents. Therefore, if you plan to merge to a single document, you should move any content in the header or footer to the document body.
You can reduce the size of the empty header and footer to give a similar appearance to the text being in the header or footer, when it is in fact in the document body (see screenshots below). To do this, click Format > Headers and Footers and adjust the Header and Footer values as you wish.
To print multiple documents in one go, please read this article.