Follow this tutorial to include header and footers in your documents.
Here's an example of a referral letter with a header and footer image attached.
In the main menu click settings
Then find the document templates button
Find Print Header Under Systems Templates, then click the pencil icon.
In the text box you can choose to write your header or upload an image
For a text header, simply type your text, format it to your liking and click save.
For an image header, click the add media icon (square with mountains)
Choose your image then click open
Once your image appears in the text box, click on the image for this dialogue to appear
Click on the box icon with the two arrows to make sure your image fits to the width of the document
Then click save
Now, back in the document templates page, click the pencil icon next to the Print Footer and repeat step 4 to add your footer text or image.
Your set header and footers will now appear in all your document templates.