// Get the first table in the document.
Table firstTable = (Table)doc.getChild(NodeType.TABLE, 0, true);

// We will split the table at the third row (inclusive).
Row row = firstTable.getRows().get(2);

// Create a new container for the split table.
Table table = (Table)firstTable.deepClone(false);

// Insert the container after the original.
firstTable.getParentNode().insertAfter(table, firstTable);

// Add a buffer paragraph to ensure the tables stay apart.
firstTable.getParentNode().insertAfter(new Paragraph(doc), firstTable);

Row currentRow;

do
{
    currentRow = firstTable.getLastRow();
    table.prependChild(currentRow);
}
while (currentRow != row);