@schiepe
Thank you for elaborating it further.
We are afraid page break may not be controlled based on some conditions. However, you may resize page contents from bottom so that empty space be ensured and then text can be added as per your requirements.
Below code snippet resizes page contents from the bottom by twenty pixels, to avoid overlapping of contents:
Document document = new Document(dataDir + "Sample.pdf");
PdfFileEditor fileEditor = new PdfFileEditor();
PdfFileEditor.ContentsResizeParameters parameters = new PdfFileEditor.ContentsResizeParameters(PdfFileEditor.ContentsResizeValue.units(0), null, PdfFileEditor.ContentsResizeValue.units(0), PdfFileEditor.ContentsResizeValue.units(0), null, PdfFileEditor.ContentsResizeValue.units(20));
fileEditor.resizeContents(document, parameters);
document.save(dataDir + "Resized_19.3.pdf");
Moreover, you may also visit Resize Page Contents for your kind reference.