Convert multiple image to PNG in Java

import com.aspose.words.*;

List<String> fileNames = Arrays.asList("Input1.png", "Input2.png");

Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);

List<Shape> shapes = fileNames.stream().map(fileName -> {
    try {
        return builder.insertImage(fileName);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}).collect(Collectors.toList());

// Calculate the maximum width and height and update page settings 
// to crop the document to fit the size of the pictures.
PageSetup pageSetup = builder.getPageSetup();
pageSetup.setPageWidth(shapes.stream().mapToDouble(shape -> shape.getWidth()).max().getAsDouble());
pageSetup.setPageHeight(shapes.stream().mapToDouble(shape -> shape.getHeight()).sum());
pageSetup.setTopMargin(0);
pageSetup.setLeftMargin(0);
pageSetup.setBottomMargin(0);
pageSetup.setRightMargin(0);

doc.save("Output.png");