Click “ Apply” to see if the border fits, otherwise play with the dimensions until fitting to taste.
Now, choose your border image and go to “ Options/Style” to the right of the thumbnails, you should choose “ Custom position/size” instead of “ Tiled”. If you choose “ Add / Import” underneath the samples and import your border image, it will be added to the samples at the end. There you have bitmap patterns, designed to be repeted/tiled as backgrounds on pages. In LibreOffice Writer it’s a bit more complicated (to my knowledge) right-click on the page, choose “ Page style…” then go to the “ Area” tab → choose “ Bitmap”. Corresponding text would be overlaid in one or more text-boxes.
Now, in LibreOffice Draw inserting a border is really easy right-click on the page, choose “ Page → Choose background image…” and you can opt for various bitmap formats or SVG-drawings. In “ Templates & Extensions” there are only few borders available (when I last checked), if you go to sites like you’ll find plenty for download, both PNG and SVG (more scalable).
