Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);
Table tab = builder.startTable();
Cell cell = builder.insertCell();
builder.insertCell();
builder.endRow();
builder.insertCell();
builder.insertCell();
builder.endRow();
builder.endTable();
tab.setPreferredWidth(PreferredWidth.fromPercent(25));
Border diagonalBorder = cell.getCellFormat().getBorders().getByBorderType(BorderType.DIAGONAL_DOWN);
diagonalBorder.setColor(Color.RED);
diagonalBorder.setLineStyle(LineStyle.SINGLE);
diagonalBorder.setLineWidth(1);
doc.save("D:\\awjava-17.3.0.docx");