Document doc = new Document("data/tableDoc.doc");

// Get the first and second table in the document.
// The rows from the second table will be appended to the end of the first table.
Table firstTable = (Table)doc.getChild(NodeType.TABLE, 0, true);
Table secondTable = (Table)doc.getChild(NodeType.TABLE, 1, true);

// Append all rows from the current table to the next.
// Due to the design of tables even tables with different cell count and widths can be joined into one table.
while (secondTable.hasChildNodes())
    firstTable.getRows().add(secondTable.getFirstRow());

// Remove the empty table container.
secondTable.remove();