Learn some HTML / CSS. This is real easy to fix in the stylesheet for the style assigned to those double lines. (Note those could be real double lines or the could be 2 single lines in a row. The treatment becomes different (and a bit trickier to avoid blank pages) for the second)
it could be as simple as (retains line)
The CSS for the line just needs one line
Code:
page-break-(before/after): always;
added to the existing styling
If you want to just SPLIT up the page (and files, which many devices treat as a new screen), the Editor has a (semi)Auto Split tool (right-click in the code, Split Multiple. IMHO this is not a pure novice tool as you do need to create a bullet proof template to detect where to ONLY do this action using solely the existing code. Simpler is to first insert a SIMPLE user made up 'marker' at the split points: eg
<split-here> (yes, that is mine), them the split tool template is easy
You can also single spilt in the Preview pane. Click the icon with a page with a line across it, the move the mouse (there will be a green line) to where: Hit 'Enter". Spin-repeat
