[shka]

Just a few thoughts about it. There are three points: integration in site/page, make it sticky on footer, fill it with content.

Following is only a prototype with limitations! Web search for "sticky footer (css)" shows dozens of possible solutions (flex, grid, js..) but you have no control over full site/ basic knowledge so I advice you this simple solution.

Sitebuilder (also new features in 5.6.2) limits positioning to content area. But best way for adding a sticky footer is inject your code below all other (also below copyright...)
So go to AdminCP

a. Create new template
Styles/StyleManager/Select Style/Choose Action/Add New Template
Title : stickyfooter
Template : test (for the moment)
Save

b. Add template hook
Products&Hooks/ Manage template hooks/Add new hook

Product : choose vbulletin
Hook is Active : mark yes
Hook Location : choose footer_before_body_end
Title : stickyfooter
Execution Order : 10
Template Name : stickyfooter (same writing as title in a.)
Save

c. Reload any forum page. At the end / last line should be "test". If not there is something wrong, ask in forum.

d. If ok edit the template from a.
Styles/Search in templates/Search for Text "stickyfooter"/Find
Choose the template from style (DblClick or edit)
Replace "test" with

<style>
#spacerforstickyfooter {
	height:50px;
	background-color:red;
	width:100%;
	margin-top:20px;
}
#stickycontainer {
	height: 50px;
	width: 100%;
	position: fixed;
	bottom: 0px;
	text-align: center;
}
#stickyfooter{
	height: 50px;
	background-color: green;
	width: 50%;
	margin: auto;
}
</style>


<div id="spacerforstickyfooter"> spacer with same height like sticky footer </div>

<div id="stickycontainer">
	<div id="stickyfooter">
		sticky footer content
	</div>
</div>

Save

e. Reload a forum page. There should be a green centered footer. Purpose of the red spacer is only that also the copyright scrolls to over the footer.
After that you can delete the background-color-definitions and adjust height/width. (height of spacer-div and container-div should be equal)

f. Replace "sticky footer content" with your content. I don't know if content is some "static pictures" or js-code given by your sponsor or so.