This java program uses Qoppa’s jPDFImages to convert a PDF to PNG image files. A PNG image is created for each page contained in the PDF document.

// open PDF document
PDFImages pdfDoc = new PDFImages ("C:\\myfolder\\input.pdf", null);
// loop through pages 
for (int count = 0; count < pdfDoc.getPageCount(); ++count)
    // convert current page to PNG at a resolution of 150 dpi
    pdfDoc.savePageAsPNG(count, "C:\\myfolder\\output_" + count + ".png", 150);