Which java API is best for converting pdf to image - scala

Question

I tried with 3 Java APIs for pdf but all 3 did not work properly.
1. PDFFile
2. PDDocument
3. PDFDocumentReader
If I have a pdf which has a 2 layer in which upper one is bit transparent, so when above 3 APIs converts it into image then only upper layer comes in image with no transparency. But both layer must come.
So suggest me other API to get my requirment fulfill
Code for PDFFile :
val raf = new RandomAccessFile(file, "r")
val channel = raf.getChannel()
val buf = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size())
raf.close()
val pdffile = new PDFFile(buf)
val numPgs = pdffile.getNumPages() + 1
for (i <- 1 until numPgs) {
val page = pdffile.getPage(i)
val pwdt = page.getBBox().getWidth().toDouble
val phgt = page.getBBox().getHeight().toDouble
val rect = new Rectangle(0, 0, pwdt.toInt, phgt.toInt)
val rsiz = resize(method, size, pwdt, phgt)
val img = page.getImage(rsiz("width"), rsiz("height"),
rect, null, true, true)
result ::= buffer(img)
Code for PDDocument :
val doc = PDDocument.load(new FileInputStream(file));
val pages = doc.getDocumentCatalog().getAllPages()
for (i <- 0 until pages.size()) {
val page = pages.get(i)
val before = page.asInstanceOf[PDPage].convertToImage()
}
Code for PDFDocumentReader :
val inputStream = new FileInputStream(file)
val document = new PDFDocumentReader(inputStream)
val numPgs = document.getNumberOfPages
for (i <- 0 until numPgs) {
val pageDetail = new PageDetail("", "", i, "")
val resourceDetails = document.getPageAsImage(pageDetail)
val image = ImageIO.read(new ByteArrayInputStream(resourceDetails.getBytes()))
result ::= image
}