Document doc = new Document("C:\\Temp\\in.docx");
Table table = (Table) doc.getChildNodes(NodeType.TABLE, true).get(0);
int count = table.getRows().getCount();
Cell cell = table.getRows().get(count - 1).getCells().get(1);
String s = cell.toString(SaveFormat.TEXT);
System.out.println(s);
Checkboes in your document are not actual checkboxxes, they are represented using special symbol, i.e. simple text. So you can only replace this symbol with another that emulates the checked checkbox.