Hello,
there is no size limit for pages in "Edit PDF", the editor always loads the whole page. If part of a page is not visible, it may be a display problem in the new editor (online since 28 October) with pages that are wider than the visible area; we are checking this. The page itself is not changed by it.
Please zoom out with "Zoom out" until the whole width of the page is visible. "Fit to view" fits the size of the first page.
If text or the border is still missing after zooming out, or if it is missing in the saved PDF, please send us a file where it happens to forum@pdf24.org so that we can reproduce this.